Model 3068A Aerosol Electrometer Instruction Manual · Product Overview 1 Model 3068A Aerosol Electrometer Unpacking and Installation 2 Instruction Manual Description 3 Operation

Model 3068A Aerosol Electrometer

Instruction Manual

P/N 1933068, Revision K January 2003

P a r t i c l e I n s t r u m e n t s

Product Overview 1

Model 3068A Aerosol Electrometer

Unpacking and Installation

2

Instruction Manual

Description 3

Operation 4

Maintenance and Service

5

Applications 6

Troubleshooting 7

Service 8

Appendixes

Manual H is tory

iv

The following is a manual history of the Model 3068A Aerosol Electrometer (part number 1933068). Revision Date

First Version October 1987 A Date unknown B May 1990 C June 1990 D November 1990 E January 1992 F January 1994 G September 1994 H May 1996 I October 1996 August 1999 J December 2000 K January 2003

In revision F, TSI’s customer service number has been changed. In revision G, the manual was revised and reformatted. In revision H, TSI’s “Limitation of Warranty and Liability” on page iii was updated. Revision I adds European Community “CE Mark” standards, revisions to Chapter 2, “Changing the Line Voltage Configuration” and “Changing Fuses,” all mentions of Model 3068 were changed to Model 3068A, and minor changes were made to rest of manual. In August 1999, TSI’s area code was changed from 612 to 651. In Revision J, Chapter 3, Chapter 7, and TSI’s Limitation of Warranty and Liability were updated. In Revision K, TSI’s address and phone numbers were updated.

v

Part Number 1933068 / Revision K / January 2003

Copyright ©TSI Incorporated / October 1987–2003 / All rights reserved.

Address TSI Incorporated / 500 Cardigan Road / Shoreview, MN 55126 / USA

Fax No. 651-490-3824

E-mail Address [email protected]

Limitation of Warranty and Liability (effective July 2000)

Seller warrants the goods sold hereunder, under normal use and service as described in the operator's manual, shall be free from defects in workmanship and material for (12) months, or the length of time specified in the operator's manual, from the date of shipment to the customer. This warranty period is inclusive of any statutory warranty. This limited warranty is subject to the following exclusions:

a. Hot-wire or hot-film sensors used with research anemometers, and certain other components when indicated in specifications, are warranted for 90 days from the date of shipment.

b. Parts repaired or replaced as a result of repair services are warranted to be free from defects in workmanship and material, under normal use, for 90 days from the date of shipment.

c. Seller does not provide any warranty on finished goods manufactured by others or on any fuses, batteries or other consumable materials. Only the original manufacturer's warranty applies.

d. Unless specifically authorized in a separate writing by Seller, Seller makes no warranty with respect to, and shall have no liability in connection with, goods which are incorporated into other products or equipment, or which are modified by any person other than Seller.

The foregoing is IN LIEU OF all other warranties and is subject to the LIMITATIONS stated herein. NO OTHER EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR PARTICULAR PURPOSE OR MERCHANTABILITY IS MADE.

TO THE EXTENT PERMITTED BY LAW, THE EXCLUSIVE REMEDY OF THE USER OR BUYER, AND THE LIMIT OF SELLER'S LIABILITY FOR ANY AND ALL LOSSES, INJURIES, OR DAMAGES CONCERNING THE GOODS (INCLUDING CLAIMS BASED ON CONTRACT, NEGLIGENCE, TORT, STRICT LIABILITY OR OTHERWISE) SHALL BE THE RETURN OF GOODS TO SELLER AND THE REFUND OF THE PURCHASE PRICE, OR, AT THE OPTION OF SELLER, THE REPAIR OR REPLACEMENT OF THE GOODS. IN NO EVENT SHALL SELLER BE LIABLE FOR ANY SPECIAL, CONSEQUENTIAL OR INCIDENTAL DAMAGES. SELLER SHALL NOT BE RESPONSIBLE FOR INSTALLATION, DISMANTLING OR REINSTALLATION COSTS OR CHARGES. No Action, regardless of form, may be brought against Seller more than 12 months after a cause of action has accrued. The goods returned under warranty to Seller's factory shall be at Buyer's risk of loss, and will be returned, if at all, at Seller's risk of loss.

Buyer and all users are deemed to have accepted this LIMITATION OF WARRANTY AND LIABILITY, which contains the complete and exclusive limited warranty of Seller. This LIMITATION OF WARRANTY AND LIABILITY may not be amended, modified or its terms waived, except by writing signed by an Officer of Seller.

Service Policy Knowing that inoperative or defective instruments are as detrimental to TSI as they are to our customers, our service policy is designed to give prompt attention to any problems. If any malfunction is discovered, please contact your nearest sales office or representative, or call TSI’s Customer Service department at 1-800-874-2811 (USA) or (651) 490-2811.

vi Model 3068A Aerosol Electrometer

Safety

vii

This section gives instructions to promote safe and proper handling of the Model 3068A Aerosol Electrometer.

!

C a u t i o n If the Model 3068A is used in a manner not specified by the manufacturer, the protection provided by the equipment may be impaired.

!

C a u t i o n No user serviceable parts inside. Refer to qualified personnel.

D e s c r i p t i o n o f C a u t i o n S y m b o l The following symbol and an appropriate caution statement are used throughout the manual and on the Model 3068A to draw attention to any steps that require you to take cautionary measures when working with the Model 3068A:

!

C a u t i o n Refer to accompanying documents.

viii Model 3068A Aerosol Electrometer

Contents

ix

Manual History........................................................................... iv

Safety ........................................................................................ vii Description of Caution Symbol.............................................. vii

About This Manual ................................................................... xiii Purpose................................................................................ xiii Organization ........................................................................ xiii Reusing and Recycling ......................................................... xiv Help! .................................................................................... xiv Submitting Comments .......................................................... xv

C h a p t e r s

1 Introduction....................................................................... 1-1 2 Unpacking and Installation ............................................... 2-1

What You Received.............................................................. 2-1 Initial Setup ........................................................................ 2-1

Protective Caps.............................................................. 2-1 Checking the Line Voltage Configuration ....................... 2-2 Changing the Fuse ........................................................ 2-3

Changing Between European and American-Style Fuses....................................................................... 2-4

Applying Power to the Electrometer ............................... 2-6 Accessories ......................................................................... 2-6

Basic Requirements....................................................... 2-6 Optional Equipment ...................................................... 2-6

Quick Check for Operability ................................................ 2-7 3 Description ........................................................................ 3-1

Principle of Operation ......................................................... 3-1 Flow Control ....................................................................... 3-3

4 Operation ........................................................................... 4-1 Concentration Meter of Singly-charged Particle

(Charger Off) .................................................................... 4-1 5 Maintenance and Service .................................................. 5-1

Calibration and Performance............................................... 5-1 Periodic Maintenance Schedule........................................... 5-1 Replacing Filter Cartridges and Cleaning the Electrometer .. 5-2 Cleaning the Flowmeters ..................................................... 5-3 Leak Testing........................................................................ 5-4

x Model 3068A Aerosol Electrometer

Electrical Adjustments ........................................................ 5-5 Electrometer Gain ......................................................... 5-5 Electrometer Zero .......................................................... 5-5 Other Electrical Adjustments......................................... 5-5

6 Applications ....................................................................... 6-1 Built-in Electrometer or Keithley Model 642 Digital

Electrometer..................................................................... 6-1 7 Troubleshooting................................................................. 7-1

Noisy Electrometer Output.................................................. 7-1 Noise at Zero Flow ......................................................... 7-1 Noise with Flow ............................................................. 7-2

8 Service ............................................................................... 8-1 Technical Contacts.............................................................. 8-1 Returning the Electrometer for Service ................................ 8-1

A p p e n d i x e s

A References ......................................................................... A-1 B Specifications ....................................................................B-1 C Schematics ........................................................................C-1

F i g u r e s 1-1 Photograph of the Model 3068A Aerosol Electrometer ....... 1-1 2-1 Power Entry, Fuse, and Voltage Module............................ 2-2 2-2 Orientation of the Voltage Selector Card ........................... 2-3 2-3 North American–Fusing Arrangement ............................... 2-4 2-4 European–Fusing Arrangement ........................................ 2-5 2-5 Fuse Block/Cover Assembly ............................................. 2-5 3-1 Schematic Diagram of the Aerosol Electrometer................ 3-1 3-2 Cross-sectional View of the Aerosol Electrometer .............. 3-2 3-3 Schematic Diagram of the Airflow System......................... 3-3

Contents xi

5-1 Vacuum Leak Testing System........................................... 5-4 5-2 Bottom View of the Model 3068A Showing the Location

of the Electrometer Gain and Zero Adjustments ............... 5-6 6-1 Charger-Electrometer Assembly Adapted for use with a

Keithley Model 642 Digital Electrometer ........................... 6-2 6-2 Cross-sectional view of the Model 3068A Electrometer

Assembly Adapted for use with a Keithley Model 642 Digital Electrometer.......................................................... 6-3

T a b l e

2-1 Components of the Aerosol Electrometer .......................... 2-1

B-1 Model 3068A Aerosol Electrometer Specifications.............B-1

xii Model 3068A Aerosol Electrometer

About This Manual

xiii

P u r p o s e The Model 3068A Aerosol Electrometer Instruction Manual is written for both the installer and the operator.

O r g a n i z a t i o n This instruction manual is organized in chapters and appendixes as follows:

❑ Chapter 1: Product Overview Gives an overview of the Electrometer.

❑ Chapter 2: Unpacking and Installation Contains information on unpacking the Electrometer and checking the contents of the shipping container.

❑ Chapter 3: Description Describes in detail the operating principles of the Electrometer.

❑ Chapter 4: Operation Describes the most commonly used operation mode of the Electrometer.

❑ Chapter 5: Maintenance and Service Describes the procedures and schedules for periodic maintenance of the Electrometer.

❑ Chapter 6: Applications Describes an application of the Electrometer for low concentration aerosols.

❑ Chapter 7: Troubleshooting Describes common difficulties that may arise when using the Electrometer.

❑ Chapter 8: Service Gives directions for contacting technical resources at TSI or returning the Model 3068A Aerosol Electrometer for service.

❑ Appendix A: References Lists references used in this manual.

❑ Appendix B: Specifications Lists specifications for the Electrometer.

❑ Appendix C: Schematics Contains three schematics for the Electrometer.

xiv Model 3068A Aerosol Electrometer

R e u s i n g a n d R e c y c l i n g

As part of TSI Incorporated’s effort to have a minimal negative impact on the communities in which its products are manufactured and used:

❑ This manual uses recyclable paper.

❑ This manual has been shipped, along with the instrument, in a reusable carton.

H e l p ! To obtain assistance with this hardware, or simply to submit suggestions, please contact Customer Service:

TSI Incorporated Particle Instruments 500 Cardigan Road St. Paul, MN 55126 USA Fax: (651) 490-3824 Telephone: 1-800-874-2811 (USA) or (651) 490-2811 E-mail Address: [email protected]

About This Manual xv

S u b m i t t i n g C o m m e n t s TSI values your comments and suggestions on this manual. Please use the comment sheet, on the last page of this manual, to send us your opinion on the manual’s usability, to suggest specific improvements, or to report any technical errors. If the comment sheet has already been used, send your comments to:

TSI Incorporated Particle Instruments 500 Cardigan Road St. Paul, MN 55126 Fax: (651) 490-3824 E-mail Address: [email protected]

xvi Model 3068A Aerosol Electrometer

C H A P T E R 1

In t roduct ion

1-1

The Model 3068A Aerosol Electrometer (Figure 1-1) is a sensitive and precise aerosol concentration sensor for measuring the output of a Model 3071A Electrostatic Classifier. The combination of a Model 3076 Atomizer, Model 3071A Classifier, and Model 3068A

Electrometer yield a highly accurate tool for producing monodisperse aerosol from a wide variety of materials with precisely known size and concentration. The optimum size range of this system is 0.01 to 0.1 micrometer. However, less precise performance is possible in the range of 0.005 to 0.01 micrometer and 0.1 to 0.5 micrometer.

Figure 1-1 Photograph of the Model 3068A Aerosol Electrometer

1-2 Model 3068A Aerosol Electrometer

This system is called a “primary” method of generating precisely known monodisperse aerosols because it depends only on basic measurements such as flow rate, voltage, and amperage. A key assumption is that all charged particles leaving the Model 3071A Classifier are “Singly charged.” Since this is not entirely true, a correlation factor K must be applied to the calculations to correct for multiply charged particles. In the range of 0.01 to 0.1 micrometer, multiply charged particles are a small fraction of the charged particles. But above 0.1 micrometer, the fraction of multiply charged particles increases sharply, limiting the accuracy of the K-factor.

A secondary feature of the Aerosol Electrometer is that it can detect the net ion concentration of sampled aerosol. This is useful in studying the health effects of ionized air. The highly sensitive Electrometer allows measurements of atmospheres that are only mildly ionized.

C H A P T E R 2

Unpacking and Insta l la t ion

2-1

This chapter contains information on unpacking the instrument and checking the contents of the shipping container. It then describes the installation procedures, available optional equipment and a quick check of operability.

W h a t Y o u R e c e i v e d The following items should be found in the shipping container: Table 2-1 Components of the Aerosol Electrometer

Qty. Description 1 Main package which contains an Electrometer current sensor and

the associated flow control and sensing circuitry (Figure 1-1) 1 Power cord 100-120 VAC, P/N 1303053 230-240 VAC, P/N 1303075 2 Extra filters, MSA 95302 Cartridge (TSI no. 1602011) 1 Instruction manual, P/N 1933068 1 Base adapter plate (for connecting a Keithley 642 Electrometer) 5 5-ft. ¼-inch poly flo tubing, TSI P/N 3929408

Check the package to be certain the shipment is complete. To operate the device, one or more of the basic accessories described above may be required.

I n i t i a l S e t u p This section contains instructions for initial setup of the Model 3068A Aerosol Electrometer. Follow the instructions in the order given.

Protective Caps Remove all protective caps from the inlet and exit flow ports, as well as from the BNC connectors.


Checking the Line Voltage Configuration The Model 3068A requires 100/120 volts AC at 0.1 amp or 230/240 volts AC at 0.05 amp with 50 to 60 hertz at any of the voltages. Use the information in this section to verify the line voltage configuration and fusing arrangement matches your local line voltages.

Check the back panel of the instrument for the voltage and fusing requirements. The label is located just above the power entry module. To change the voltage setting, follow these steps:

1. Disconnect the power from the Model 3068A and remove the line cord. Locate the power-entry module on the back panel of the Model 3068A (Figure 2-1).*

2. Lift off the cover of the fuse and voltage module cover on the back panel of the Model 3068A using a small-blade screwdriver or similar tool (Figure 2-1). Set aside the cover/fuse block assembly.

Figure 2-1 Power Entry, Fuse, and Voltage Module

3. Grasp the indicator pin and pull the voltage-selector card straight out of the housing (Figure 2-1).

4. Orient the selector card so that the desired voltage is readable at the bottom.

*Drawings reprinted by permission of Corcom Incorporated, Libertyville, Illinois.

Unpacking and Installation 2-3

5. Orient the indicator pin so that it points up when the desired voltage is readable at the bottom. When the pin is fixed and in place, rotate the card 90° clockwise (Figure 2-2).

Figure 2-2 Orientation of the Voltage Selector Card

6. Insert the voltage-selector card into the housing, making sure the edge containing the desired voltage is inserted first and the printed side of the card faces the IEC (power cord) connector.

7. Replace the cover, making sure that the indicator pin shows the desired voltage.

Changing the Fuse

1. Disconnect the power from the Model 3068A and remove the line cord.

2. Lift off the power-entry module on the back panel of the Model 3068A using a small-blade screwdriver or similar tool (Figure 2-1).

3. Replace the fuses. Make sure the Fuse(s) are the proper size and rating for the line voltage you are using. The Fusing label is located just above the power entry module on the back panel of the Model 3068A.


Note: Two European-style 5 × 20 mm fuses are required in the European-Fusing arrangement (Figure 2-4).

4. Replace the power-entry module cover. Changing Between European and American-Style Fuses Before installing the Model 3068A, make sure the fuse is compatible with your site. The Model 3068A works with both North American and European-style fuses. The 100/120-volt model comes with the North American-style fuse and the 230/240-volt model is equipped with the European-style fuse. If you need to change the fuse from North American (Figure 2-3) to the European style (Figure 2-4),or vice versa, follow these steps:

1. Disconnect the power from the Model 3068A and remove the line cord.

2. Lift off the power-entry module on the back panel of the Model 3068A cover using a small-blade screwdriver or similar tool.

Jumper Bar

Fuse Block Cover

Fuse

Figure 2-3 North American–Fusing Arrangement


Fuse Block

Cover

Fuses

Jumper Bar

Figure 2-4 European–Fusing Arrangement 3. Loosen the screw on the fuse block two turns.

4. Remove the fuse block (Figure 2-5) by sliding it up and away from the screw. Lift the block from the pedestal.

FuseFuse Block

Cover Figure 2-5 Fuse Block/Cover Assembly

5. Change the fuses:

Note: Two European 5 × 20 mm fuses are required in the European-Fusing Arrangement.

Invert the fuse block and slide it back onto the screw and the pedestal.

6. Tighten the screw and replace the power-entry module cover. The fuse(s) that enters the housing first is the active one.


Applying Power to the Electrometer Plug the power cord into the connector on the back panel and then plug it into the AC power source. Apply power to the Electrometer with the switch next to the power cord on the back panel.

A c c e s s o r i e s The following lists the basic requirements and the optional equipment for the Aerosol Electrometer.

Basic Requirements The Aerosol Electrometer is designed to operate with sampling rates up to 10 liters per minute. The pressure drop across the instrument at this flowrate is about 22 centimeters of water. For laboratory use, the system can often be connected directly to an existing vacuum source in the laboratory. If this is not feasible, use a TSI Model 3033 Vacuum Pump or Gast Model 0522 oil-less vacuum pump for this purpose. Avoid piston or diaphragm pumps because they produce pulsing flow that causes greater measurement errors. The unit is normally operated in the underpressure mode whereby the aerosol is drawn into the instrument with a vacuum pump. However, it can also be operated in the overpressure mode whereby the aerosol is pushed into the instrument.

Optional Equipment The instrument’s built-in Electrometer has a noise current of approximately 1 x 10–15 amperes. If you prefer a lower noise current, directly connect the instrument to a Keithley Model 642 Digital Electrometer (28775 Aurora Road, Cleveland, OH 44139 USA, 1-216-248-0400). Under this operating condition, the noise current is reduced to 1 × 10–17 amperes.


The Aerosol Electrometer can be used together with the Model 3071A Electrostatic Classifier for generating monodisperse aerosol of known size and known concentration.

Q u i c k C h e c k f o r O p e r a b i l i t y Follow these steps to check the operability of the Electrometer:

1. Connect the power cord to the correct line voltage.

2. Switch on the power.

3. Rotate the Selector Knob to Aerosol Current; the meter reading should be stable at ±0.001 volt. The aerosol current reading should be near zero or slightly positive—but not negative.

4. Rotate the Selector Knob to Aerosol Flow; a stable meter reading at ±0.005 volt should be displayed.

5. Close the Vacuum Adjust Valve by turning the valve clockwise to stop. Remove the protective cap from the inlet of the instrument.

6. Connect a vacuum pump to the Vacuum Connector on the front panel.

7. Connect a high-efficiency filter to the aerosol inlet fitting.

8. Rotate the Meter/Output Selector to Aerosol Flow and slowly open the Vacuum Adjust Valve until the voltage reading on the meter corresponds to 5 liters per minute of aerosol flow.

9. Rotate the Meter/Output Selector to Aerosol Current. The meter reading should now drop below +0.005 volt if the Electrometer has been properly zeroed (see “Electrical Adjustments” in Chapter 5).


C H A P T E R 3

Descr ip t ion

3-1

This chapter describes in detail the operating principles of the instrument. It then gives details on the flow control used in the instrument and some operating characteristics and precautions that you should be aware of.

P r i n c i p l e o f O p e r a t i o n The Aerosol Electrometer measures the ion concentration of the sampled airstream. This mode is normally used to accurately measure the concentration of monodisperse, singly charged particles flowing out of the Model 3071A Electrostatic Classifier. It may also be used to measure the net ion concentration of sampled air. The Aerosol Electrometer consists of an Electrometer current sensor which collects the particles by filtration and measures the total electrical current with an Electrometer. Figure 3-1 is a schematic diagram and Figure 3-2 is a cross-sectional view of the Electrometer current sensor. The current sensor is similar to the corresponding component in the Model 3030 Electrical Aerosol Size Analyzer described by Sem (1975) and Liu and Pui (1975).

AerosolFlowmeter

SampleAdjustValve

ToVacuumSupply

AerosolInlet

AerosolFilter

Electrometer

AerosolFlowrate

AerosolCurrent

Figure 3-1 Schematic Diagram of the Aerosol Electrometer


Charged aerosol enters the Electrometer current sensor through a metal cover which shields the Electrometer input from stray electric fields. In the Electrometer current sensor, an absolute filter removes the charged particles from the airstream. The filter is mounted on a Teflon® insulator within an enclosed metal housing and connected to the input of a solid-state Electrometer operational amplifier. A 1011-ohm resistor of 1 percent accuracy is used as a feedback resistor for the amplifier. An additional 10:1 voltage divider is incorporated in the feedback path to obtain an overall effective feedback resistance of 1012 ohms. The Electrometer has an output voltage range of 0 to 10 volts, corresponding to a current range of 0 to 10 picoamperes. The noise current of the Electrometer is approximately 1 × 10–15 amperes.

Figure 3-2 Cross-sectional View of the Aerosol Electrometer The base of the current sensor is designed so that the sensor can be directly connected to the input of the Keithley Model 642 Digital Electrometer (see “Concentration Meter of Singly-charged Particles” in Chapter 4 for converting instructions). Under this operating condition, the noise current is reduced to less than 5 x 10–16 amperes.

Description 3-3

The current I measured by the Electrometer is related to the input aerosol concentration N by equation (1):

I = N np e qe (1) where np (number of elementary charge units) is the particle charge, e (= 1.6 × 10-19 coulomb) is the elementary unit of charge, and qe (cm3/s) is the volumetric aerosol flowrate into the Electrometer current sensor. When the particle charge is known, the aerosol concentration can be calculated from equation (1).

F l o w C o n t r o l The flow system for the Aerosol Electrometer is shown schematically in Figure 3-3. The particle loss through the inlet is negligible for sizes below 3 micrometers in diameter. The high-efficiency aerosol filter in the airstream ahead of the flowmeter protects the thermal flowmeter from contamination. The flowmeter is described below. The vacuum-adjust valve downstream of the flowmeter allows you to control the sample rate.

Aerosol Flowmeter

Sample Adjust Valve

To Vacuum Supply

Aerosol Inlet

Aerosol Filter

Figure 3-3 Schematic Diagram of the Airflow System


T h e r m a l A e r o s o l F l o w m e t e r The aerosol flowmeter is a Model 4140 Thermal Mass Flowmeter. The Thermal Mass Flowmeter has a linear output of 0–10 volts corresponding to 0–10 lpm.* The output is accurate to 2% of reading and has a response time of 4 ms. Periodically inspect the flow sensor by looking into the outlet of the flowmeter. Remove dust, particles, and fibers from the sensor with clean, dry compressed air. The flow sensor will break if touched. Never run liquids through the flowmeter and never touch the sensor with a brush. Dust or other deposits on the flow sensor will degrade the 4140’s flow accuracy.

CAUTION

!

The flowmeter must be switched off for cleaning. Only use clean, dry, compressed air when attempting to remove contamination from the sensor.

Because thermal flow sensors are sensitive to changes in air density and air velocity, all thermal flowmeters indicate flowrates with reference to a set of standard conditions. For TSI instruments, standard conditions are defined as 21.1° C (70° F) and 101.3 kPa (14.7 psia). Other manufacturers may use different values. Standard flowrate is the flowrate the air would be moving if the temperature and pressure were at standard conditions. It is usually the most useful measure of airflow because it defines the heat-carrying capacity of the air. Volumetric flowrate is the true volume flow of the gas exiting the flowmeter. In some instances, volumetric flowrate rather than standard flowrate may be of interest. To display volumetric flowrate, the Model 4140 will multiply the standard flow measurement by the following density correction factor:

m

m

P

TStdFlowFlowVolumetric

3.10111.2115.273

15.273)(

++=

*The display on the front panel has a .000–.015 volt offset at zero flow due to the display circuitry.

Description 3-5

Where

Tm = Gas temperature measured in flow tube in units of degrees Celsius Pm = Absolute pressure measured in flow tube in units of kPa

To demonstrate the difference in output, consider the following. Measured flow displays 10 Std L/min at 15°C and 117 kPa. The volumetric flow as calculated by the Model 4140 would be as follows.

min/478.8117

3.10111.2115.273

1515.273)10( LFlowVolumetric =

++=


C H A P T E R 4

Operat ion

4-1

This chapter describes the most commonly used operation mode of the instrument. For other operating applications, see Chapter 6, “Applications.”

C o n c e n t r a t i o n M e t e r o f S i n g l y - c h a r g e d P a r t i c l e ( C h a r g e r O f f )

The Aerosol Electrometer is used to measure the concentration of singly charged particles from the Model 3071A Electrostatic Classifier. Follow these ten steps for measuring the particle concentration: 1. Connect the power cord to the correct line supply (see “What

You Received” in Chapter 2).

2. Shut off the Vacuum Adjust Valve by turning the knob clockwise in order to stop; then connect a vacuum pump (TSI Model 3033, Gast Model 0522, or equivalent) to the Vacuum Connector.

3. Switch on the power for both the Aerosol Electrometer and the vacuum pump.

4. Rotate the Meter/Output Selector to Aerosol Flow and open the Vacuum Adjust Valve slowly until the meter reading corresponds to the desired operating flow.

5. Connect the aerosol source to the inlet on the front of the instrument.

6. Flip the Meter Range switch to the 10V position and the Meter/Output switch to Aerosol Current.

7. The meter display in volts is the current resulting from the collection of the singly charged particles on the filter: 1 volt = 10–12 amperes.

8. The particle concentration for singly charged particles can be calculated from equation (3):

N = I/qe e (3)

where N (particles/cm3) is the particle concentration, I (amp) is the Electrometer current, qe (cm3/s) is the aerosol flowrate and e = 1.6 × 10–19 coulomb is the elementary unit of charge.


9. To monitor the Electrometer current continuously with a strip-chart recorder, simply make an electrical connection between the recorder input and the Aerosol Current Output BNC connector.

10. If the meter indicates nearly 10V, flip the meter range switch to the 100V position. The decimal point automatically indicates the correct voltage up to 100 volts = 100 × 10–12 amperes.

C H A P T E R 5

Maintenance and Serv ice

5-1

This chapter describes the procedures and schedules for periodic maintenance of the Electrometer. The maintenance includes filter changes, cleaning, leak checking and electrical adjustments on the instrument.

C a l i b r a t i o n a n d P e r f o r m a n c e After electronic checkout and adjustment, each Aerosol Electrometer being calibrated at the factory is compared with a factory standard Aerosol Electrometer while sampling the output of a Model 3071A Electrostatic Classifier. All new and repaired Aerosol Electrometers must agree with the factory standard within 5 percent. Most instruments agree within 2 percent if the flowrates are carefully adjusted.

P e r i o d i c M a i n t e n a n c e S c h e d u l e Periodic cleaning of several portions of the Aerosol Electrometer is necessary to ensure proper performance. Accumulation of aerosol deposit on the Teflon insulator in the Electrometer aerosol filter assembly will cause current leakage to ground, resulting in incorrect current measurement. Plugging of the high-efficiency filter will result in high pressure drop through the system, causing error in the measurement of volumetric flowrates. The service intervals depend on the aerosol concentration entering the unit. Normal aerosols with current levels of 0.5 to 1.0 × 10–12 amperes require maintenance according to this schedule: Replace the aerosol filter cartridge every 200–500 hrs of operation Clean the entrance-tube assembly every 500–1000 hrs of operation Clean the flowmeter every 500–1000 hrs of operation


R e p l a c i n g F i l t e r C a r t r i d g e s a n d C l e a n i n g t h e E l e c t r o m e t e r

See the previous section “Periodic Maintenance Schedule” for a suggested schedule for filter replacement and Electrometer cleaning. Follow these 16 steps to replace the filter cartridge and clean the Electrometer. Note: Refer to schematic 9080935 for reference numbers.

1. Disconnect the AC power cord from the instrument.

2. Remove the sheet-metal cover from the instrument by withdrawing all screws on each side.

3. Refer to the exploded view of the main mechanical assembly (Schematics 9080934 and 9080935) in Chapter 6.

4. Withdraw the four screws (6–32 UNC, ref. #21-22) from base flange of 1502194 (ref. #9).

5. Remove the entire assembly (1502194, ref. #9) and attached fitting from the cabinet, exposing the filter cartridge (1602011, ref. #13) and its mounting parts.

6. Hold mounting (1502171, Ref #14) firmly and unscrew cartridge (1602011, ref. #13). Do not twist 1502171 (ref. #14) on its mounting (1502172, ref. #14).

7. Unsolder the electrical lead from the mounting (1502171, ref. #14), unscrew special nut (1502160, ref. #4) and lift mounting (1502171, Ref. #14) from the assembly.

8. Remove the visible upper Teflon insulator (1502172, ref. #5). The O-ring seal may stick; work the Teflon insulator back and forth until it comes out.

9. Clean the upper insulator (1502172, ref. #5) using detergent and water in an ultrasonic cleaner. Rinse with clean water; then rinse with clean reagent-grade alcohol. Air dry and reinstall the upper insulator, using a moderate amount of high-vacuum grease on the O-ring. Do not touch upper insulator (1502172, ref. #5) with bare fingers after cleaning and do not apply vacuum grease anywhere except to the O-ring.

Maintenance and Service 5-3

10. Clean the filter mounting (1502171, ref. #14) and replace it in the assembly, being careful to tighten nut (1502160, ref. #4) about one-half turn past finger-tight.

11. Solder the end of the electrical lead on center conductor (SA0397) to the filter mounting (1502171, ref. #14).

12. Install a new filter cartridge element (1602011, ref. #13), holding the filter mounting (1502171, ref. #14) firmly during tightening.

13. Clean the Electrometer housing (1502194, ref. #9) and the aerosol inlet fittings.

14. Grease the O-ring (2501237, ref. #19) lightly with high-vacuum grease and reinstall the entire housing (1502194, ref. #9) and attached fittings.

15. Leak-test the assembled instrument as described in Chapter 5, “Leak Testing.”

16. Verify that the instrument is working properly as described in Chapter 2, “Quick Check for Operability.”

C l e a n i n g t h e F l o w m e t e r s Although the response of the thermal flowmeter normally returns to within about ±2 percent of the original calibration with careful cleaning, it is always best to check the calibration immediately after cleaning. Use a trusted “standard” flowmeter, for example, the Gilibrator-2 wet cell flowmeter manufactured by:

Sensidyne Incorporated 16333 Bay Vista Drive Clearwater, Florida 33760 Telephone: 727-530-3602 Fax: 727-539-0550 Toll Free: 1-800-451-9444


L e a k T e s t i n g Whenever an air leak is suspected or a significant part of the air flow system has been reassembled, a leak test is necessary to assure proper performance. Follow these four steps:

1. Plug the aerosol inlet.

2. Connect a vacuum pump, valve, and an accurate vacuum gauge to the vacuum connector as shown in Figure 5-1.

Figure 5-1 Vacuum Leak Testing System

3. Draw a vacuum of 500–600 mm Hg into the Aerosol Electrometer. Tightly close the valve and observe the vacuum gauge. The vacuum in the system must not drop faster than 1 millimeter Hg every 2 minutes.

4. If the vacuum pressure decreases too rapidly, apply several drops of clean isopropyl alcohol to suspected leaking joints. If a leak exists, the alcohol is quickly drawn into the joint. If no leak exists, the alcohol will remain in the joint until it evaporates. Apply a moderate amount of high-vacuum grease, such as Dow Corning High-Vacuum Grease (No. 970V), to all O-rings when reassembling any part of the Aerosol Electrometer. However, be careful not to overgrease.

Maintenance and Service 5-5

E l e c t r i c a l A d j u s t m e n t s This section describes the electrical adjustments that are available on the Electrometer.

Electrometer Gain The sensitivity of the Electrometer can be switched between two values: (a) 1 picoampere/volt or (b) 10 picoamperes/volt. The more sensitive a value has a noise level of about ±1 × 10–15 ampere, while the less sensitive b range has a noise level of about ±10 × 10-15 ampere and is used only for higher aerosol concentration when the aerosol current is greater than 10 × 10–12 amperes. To switch to the other sensitivity, flip the slide switch (shown in Figure 5-2). The switch is accessible through a hole in the bottom of the Aerosol Electrometer.

Electrometer Zero Zero the Electrometer in the sensitivity (gain) position you are operating. Stop all aerosol flow. Switch to the Aerosol Current. The zero potentiometer is accessible through a hole in the bottom of the Aerosol Electrometer shown in Figure 5-2. Using a small, slotted screwdriver, adjust the zero until the Aerosol Current readout is 0 ±1 in the last visible digit.

Other Electrical Adjustments If other electrical adjustments are needed, contact the TSI factory. A qualified electrical technician should refer to the circuit diagram (Appendix C), the circuit board assembly layout, and the panel meter instruction sheet (appendix).


Figure 5-2 Bottom View of the Model 3068A Showing the Location of the Electrometer Gain and Zero Adjustments

C H A P T E R 6

Appl icat ions

6-1

This chapter describes an application of the Electrometer for low concentration aerosols. A method is described to increase the sensitivity of the sensor using a Keithley Model 642 Digital Electrometer.

B u i l t - i n E l e c t r o m e t e r o r K e i t h l e y M o d e l 6 4 2 D i g i t a l E l e c t r o m e t e r

The built-in Electrometer, an Analog Devices Model 310J operational amplifier, has a noise level between 1 and 2 × 10–15 amperes. With the Keithley Model 642 Digital Electrometer, an overall noise level of less than 5 × 10–16 amperes can be achieved. If the aerosol current levels being measured are low, below 100 × 10-15 amperes, you may substitute a Keithley Model 642 Digital Electrometer. To adapt the Aerosol Electrometer to a Keithley Model 642 Digital Electrometer, follow these 11 steps:

1. Disconnect the AC power cord and remove the sheet-metal cover from the cabinet.

2. Remove the thermal flowmeter by disconnecting the tubing at each end and removing the flowmeter bracket.

3. Refer to the exploded view of the main mechanical assembly (Schematics 9080934 and 9080935) later in this chapter and to the exploded view of the main mechanical assembly adapted for the Keithley Model 642 Digital Electrometer (Figure 6-1).

4. Disconnect the electrical cable near the bottom of the main assembly.

5. Remove the main assembly from the cabinet by removing three larger screws from the bottom of the Aerosol Electrometer floor and lifting the assembly out.


6. Remove the built-in Electrometer assembly as follows:

a. Remove plate (1502175).

b. Remove the operational amplifier and Electrometer circuit board by withdrawing six screws (6–32 UNC × 3⁄8) and lifting the circuit assembly.

c. Remove the Electrometer housing (1502186) by withdrawing the four screws that connect the housing to the main flange of the Electrometer (1502185).

Figure 6-1 Charger-Electrometer Assembly Adapted for use with a Keithley Model 642 Digital Electrometer. Refer to Schematics 9080934 and 9080935, to remove analog devices Electrometer assembly.

7. Attach the Keithley adapter (1502176) to the Electrometer’s main flange (1502185) using four screws (6–32 UNC). Be sure two O-rings (2501024 and 2501032) are in place on the flange (1502176).

Applications 6-3

8. Install the O-ring to the Keithley adapter (1502176).

9. Set the main charger-Electrometer assembly on to the Keithley Model 642 Digital Electrometer sensing head as shown in Figure 6-2.

Figure 6-2 Cross-sectional view of the Model 3068A Electrometer Assembly Adapted for use with a Keithley Model 642 Digital Electrometer

10. Reconnect the main assembly to the Aerosol Electrometer cabinet as follows:

a. Connect the thermal flowmeter entrance to the fitting at the bottom of the main assembly. (Use extra Imperial Eastman 44-P-¼ tubing shipped with your Aerosol Electrometer, as needed.)

b. Connect the thermal flowmeter exhaust to the side fitting (inlet) of the vacuum adjust valve.

c. Leave the 4-conductor cable near the bottom of the main circuit board unconnected.

11. Operate the Aerosol Electrometer normally, except obtain aerosol current measurements from the Keithley Model 642 Digital Electrometer. (See the Keithley Model 642 Digital Electrometer operator’s manual for instructions on its use.) The minimum noise levels are obtained in the Keithley’s damped mode and charge accumulation modes.


Applications 6-5


C H A P T E R 7

Troubleshoot ing

7-1

This chapter describes common difficulties that may arise when using the Electrometer. Suggestions are given for abnormal noise with no flow, noise with flow and using the thermal flowmeter.

N o i s y E l e c t r o m e t e r O u t p u t The Electrometer current sensor in the Aerosol Electrometer has an electrical noise level of 1 to 2 × 10–15 amperes with the Analog Devices brand operational amplifier. When connected to a Keithley Model 642 Digital Electrometer, the damped noise level is less than 1 × 10–15 ampere. Such low noise levels require very careful design to provide sufficient shielding and insulation.

Noise at Zero Flow If the Electrometer (Aerosol Current) exhibits excessive random noise at zero flow (more than ±2 millivolt on the digital voltmeter), the problem is probably a poor electrical connection or an electrical leakage path to ground. The first step is to check terminal 3 (see Appendix C, Schematic Dwg. No. 9060220) on the circuit board to be certain the noise is coming from the Electrometer. If it is, then expose the aerosol collecting filter (1602011) from the Electrometer assembly and thoroughly clean the upper Teflon insulator (1502172) (see Chapter 5 for cleaning instructions). A second possible problem is charge leakage across the outer surface of the 1011-ohm resistor or its associated capacitor on the Electrometer assembly as well as insulation paths on the input line. Clean all suspected leakage paths, including the surface of the 1011 ohm resistor, using clean reagent-grade alcohol. If the Electrometer noise is 60 Hz (or 50 Hz if your line voltage is 50 Hz), then grounding points on the entire assembly should be checked. If the noise appears at the output but not at the input of the electrical filtering network on the circuit board, then check the electrical filter circuit itself.


If the electrical noise of the Electrometer persists, check the Analog Devices operational amplifier. Do not ground the input; either let it float or install a large resistor (a 109 ohm resistor will give a voltage gain of 100) in series with the input and ground it. With this resistor, the amplifier can be checked for linearity by applying a voltage input to make sure it is operating properly.

Noise with Flow Generally, noise that is present only when the flow is on is not an Electrometer problem, but rather a problem with fluctuations in the aerosol concentration level. However, to check this, connect a high-efficiency particle filter to the aerosol sample inlet so that the measured aerosol concentration goes to nearly zero. The noise fluctuations will then normally disappear.

C H A P T E R 8

Serv ice

8-1

This chapter gives you information you need to contact technical personnel or Customer Service at TSI or to return the Model 3068A Aerosol Electrometer for service.

T e c h n i c a l C o n t a c t s ❑ If you have any difficulty setting up or operating the

Electrometer, or if you have technical or application questions about this instrument, contact an applications engineer at TSI Incorporated, (651) 490-2811.

❑ If the Electrometer does not operate properly, or if you are returning the instrument for service, contact TSI at 1-800-874-2811 (USA) or (651) 490-2811.

R e t u r n i n g t h e E l e c t r o m e t e r f o r S e r v i c e Call TSI at 1-800-874-2811 (USA) or (651) 490-2811 for specific return instructions. Customer Service will need this information when you call:

❑ The instrument model number

❑ The instrument serial number

❑ A purchase order number (unless under warranty)

❑ A billing address

❑ A shipping address. Use the original packing material to return the instrument to TSI. If you no longer have the original packing material, ensure the panel controls, indicators, and connectors are protected.


A P P E N D I X A

References

A-1

1. Agarwal JK and GJ Sem [1978] “Generating Submicron Monodisperse Aerosols for Instrument

Calibration” TSI Quarterly, Vol. IV, No. 2, TSI Incorporated, Box 43394,

St. Paul, Mn. 55164. 2. Liu BYH and DYH Pui [1975] “On the Performance of the Electrical Aerosol Analyzer” J. Aerosol Sci. 6, 249–264. 3. Liu BYH and DYH Pui [1974] “A Submicron Aerosol Standard and the Primary, Absolute

Calibration of the Condensation Nuclei Counter” J. Colloid Interface Sci. 47, 155–171. 4. Liu BYH and DYH Pui [1977] “On Unipolar Diffusion Charging of Aerosols in the Continuum

Regime” J. Colloid Interface Sci. 58, 142. 5. Liu BYH and KW Lee [1975] “An Aerosol Generator of High Stability” Am. Ind. Hyg. Assoc. J. 36, 861–865. 6. Liu BYH and KW Lee [1976] “Efficiency of Membrane and Nuclepore Filters for

Submicrometer Aerosols” Environ. Sci. Technol. 10, 345–350. 7. Liu BYH and GA Kuhlmey [1977] “Efficiency of Air Sampling Filter Media in X-Ray Fluorescence Analysis of Environmental Samples” P. 107-119, (T.G. Dzubay, ed.), Ann Arbor Science Publishers,

Inc. Ann Arbor, Mich. 8. Pui DYH [1976] “Experimental Study of Diffusion Charging of Aerosols” Ph.D. Thesis, Mechanical Engineering Department, University

of Minnesota, Minneapolis, Minnesota.

A-2 Model 3068A Aerosol Electrometer

9. Sem GJ [1975] “Design and Application of An Electrical Size Analyzer for

Submicron Aerosol Particles” Analysis Instrumentation, Vol. 13, Proceedings of the 21st

Annual ISA Analysis Instrumentation Symposium, Instrument Society of America, 400 Stanwix St., Pittsburgh, Pa. 15222.

10. Sinclair D, RJ Countess, BYH Liu and DYH Pui [1979] “Automatic Analysis of Submicron Aerosols” Chapter in Aerosol Measurement D.A. Lundgren, M. Lippmann, F.S. Harris, Jr., W.E. Clark,

W.H. Marlow, editors, University of Florida Press, Gainesville, Florida.

11. Sverdrup GM [1977] “Parametric Measurement of Submicron Atmospheric Aerosol

Size Distribution” Ph.D. Thesis, Mechanical Engineering Department, University

of Minnesota, Minneapolis, Minnesota.

A P P E N D I X B

Speci f icat ions

B-1

Table B-1 gives the specifications for the Model 3068A Aerosol Electrometer. Note: The specifications in Table B-1 are subject to change without

notice.

Table B-1 Model 3068A Aerosol Electrometer Specifications

Mode of operation ......................... Particle concentration or charge via electrostatic measurement

Particle size range ......................... 0.002–5 µm

Particle type .................................. Solids and nonvolatile liquids

Aerosol sample rate ....................... 10 L/min maximum

Flowmeter ...................................... Thermal flowmeter, 0–25 lpm

Output ........................................... Total air flow ...................................Aerosol current ...............................

4 digit LED display and analog voltage 0.015 to 10V = 0–10 lpm 0.001 to 10V

Noise level of electrometer ........... 2 × 10–15 ampere (when used with Cary 401 Electrometer, not included, noise is <10–15 ampere) 10–15 ampere is the result of 188 singly charged particles per cm3 at a flowrate of 2 lpm

Power requirements ...................... 100/120/230/240 VAC 0.1/0.1/.05/.05 Amps 50 to 60 Hz at any voltage

Fuse requirements ......................... 100/120V ~ T .25A, SB/250V 230/240V ~ T 0.125A, SB/250V

Dimensions .................................... 304 × 213 × 196 mm (LWH) 12 × 8.4 × 7.7 in.

Weight ............................................ 16.6 kg 14 lbs 9 oz

Environmental conditions ............ Indoor use Altitude up to 2000 m (6500 ft) Ambient temperature 5–40°C Ambient humidity 0–90% RH noncondensing Overvoltage category II Pollution degree II

B-2 Model 3068A Aerosol Electrometer

A P P E N D I X C

Schemat ics

C-1

The following schematics are enclosed: 9060220, Revision A 9080933, Revision C 9080941, Revision A

C-2 Model 3068A Aerosol Electrometer

Applications C-3


Applications C-5


TSI Incorporated 500 Cardigan Road, Shoreview, MN 55126 U.S.A. Web: www.tsi.com

Documents

Model 3068A Aerosol Electrometer Instruction Manual · Product Overview 1 Model 3068A Aerosol Electrometer Unpacking and Installation 2 Instruction Manual Description 3 Operation