Dynamic Balance Procedure - Teledyne 212R Instruction Manual

Thermal conductivity analyzer

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Table of Contents

Thermal Conductivity Analyzer

The measuring bridge circuit (see schematic) incorporates two 10 turn

potentiometers that are utilized to compensate for minute differences in the

resistive and reactive properties of the hot wire elements and the center

tapped secondary of the bridge transformer in the reference and zero gas

related to the application.

The potentiometers are of the screw driver adjustment type and are

equipped with shaft locking assemblies that have been factory adjusted to create

enough friction so that the shaft will not change position in shipment. The potenti-

ometers are located on the amplifier chassis, and are controlled through two

holes identified "RESISTIVE" and "REACTIVE" on the inner control panel.

DO NOT OPEN THE INNER PANEL OF THE ANALYZER TO

GAIN ACCESS TO THESE CONTROLS. The balance adjustments

should not be disturbed if the analyzer is not up to operating temperature.

Correct bridge balance can only be achieved at operating temperature be-

cause of the inherent thermal junctions within the potentiometers themselves.

The minute voltages produced by contact between the dissimilar materials

within the potentiometers are effectively balanced out in the procedure when

it is accomplished at operating temperature. Because the voltage generated

by these junctions varies with temperature, and because the analyzer will

resolve a 0.25 microvolt change in bridge voltage, temperature stability is a

mandatory prerequisite to the dynamic balance procedure.

To restore zero control within the limits of Range # 1, employ the

following Procedure:

1) With zero gas flowing, adjust the sample and reference gas flowme-

2) Set the ZERO potentiometer to 500.

3) Connect a voltmeter to the instrument signal output. Connect an

4) If a reading of +15 or –15 volts is indicated on the oscilloscope

6.2.1