Med. & kiol Engng. Vo[. 6, pp. 553-554. Pergarnon Press, 1968. Printed in Great Britain

TECHNICAL NOTE

A TRANSISTORIZED ROTAMETER*

SIMULTANEOUS electrical registration of data obtained from isolated organs is often very difficult. Especially, the registration of the perfusion fluid flow is one of the most troublesome and expensive problems.

The transistorized rotameter which has been developed to measure the perfusion flow of isolated spleen prepara- tions may bring a suitable solution for measurements of this kind in other techniques.

The apparatus has two parts: (a) The rotarneter which consists of a cylindrical

Perspex body having a major outside diameter of 14 m m and a length of 70 ram.

A conical bore of 31 mm is made at the topside of the body and is drilled with a conical reamer of 4-5 mm/5 per cent (DIN 9) to give the proper size and shape to the bore. The remaining part of the body is drilled with a normal drill of 3"2 mm (Fig. 113).

The float is made from an annealed and silvered iron wire having a diameter of 1 mm and a length of 27 mm. I t bears at the top a Perspex double conical disc of which the diameter is 4.2 m m and the thickness 4 mm. The weight of the float is 0.23 g. A hood with an O-ring

gasket (Parker O-ring No. 2-10) is screwed on the top of the rotameter and prevents leakage of fluid.

Two coils are wound around the outside of the rota- meter body. The first (excitation) coil is made of 500 turns of enamelled wire (0"1 mm in diameter) wound in a groove of 3.5 mm wide and 3 m m deep situated at about the middle of the rotameter body. The second (pick-up) coil is a 3-1ayer winding of 600 turns of the same wire close wound around the lower part of the rotameter. This winding space has been previously reduced to a diameter of 6 rnm. The coils are thoroughly varnished with Araldite (Ciba-PZ 820/HZ 820).

(b) The electrical part (Fig. 1A) of the rotameter consists of a Colpitts-uscillator using a transistor (type AC 128 or equivalent) and is mounted on an epoxy board of 75 by 75 ram. Printed wiring is used throughout. The oscillator is fed by a 6 V battery and produces a sine wave of ~z 5 V peak to peak at a frequency of 25 kHz over the excitation coil.

The rotameter is mounted on the epoxy board by means of two Perspex fittings.

The pick-up coil is connected to a detecting device

_• B

" - o O-ring ~ r m r

AC128 47K'-t- ~ Excitation r I~./J ~.//J 1 Izcro setting

l~G. 1

* Received 19 February, 1968.

553

554 TECHNICAL NOTE

formed by a diode (OA 81 or equivalent) and a smoothing condensor of 0"047 ~tF. (Fig. 1C).

The d.c.-voltage variation obtained with the full displacement of the float is • 50 mV.

The range of the flowmeter is 10-100 ml/min and there is a perfect linearity from 20 to 80 ml/min.

Besides the coupling of the two coils due to the iron wire of the float there is also a mutual inductance which produces a constant d.c.-voltage after detection. This voltage has to be eliminated, which can easily be done by compensating it (zero setting). The off-set voltage is

produced in a potentiometric circuit and placed in opposition to the detected potential. (Fig. IC).

Both sides of the completed epoxy board are thoroughly varnished with Araldite to protect them against corrosion.

A. L. DELAUNOIS J. 17. and C. Heymans Institute for Pharmacology of the University of Ghent Albert Baertsoenkaai 3 Ghent Belgium