Teledyne 238 - Thermal conductivity analyzer - Manual (Page 35)

4-17 TELEDYNE BROWN ENGINEERING
Analytical Instruments
Thermal Conductivity Analyzer Linearizer 4
4.4 How to Use the Linearizer
Refering to Figure 4-10 for positioning of the Linearizer components,
check to see that the proper breakpoint resistors are installed. Also, refer to
the Linearizer drawings that have been included in the Appendix.
4.4.1 Nulling Amplifiers A1A
1. Short the input (pin 3) to the common of the diff. power
supply.
2. Connect a DVM to TP1 (testpoint 1 is located on the PC
board)
3. Adjust trimpot P9 until the DVM reads 0 mV ±10 mV.
4.4.2 Nulling the Entire Linearizer Input to Output
1. Maintain the shorted input of A1A. (See step 1 above.)
2. Connect the DVM to the output of the linearizer (pin 7
of A3B).
3. Adjust trimpot P10 until the DVM reads 0 mV ±10 mV.
4.4.3 Linearizing the Calibration Curve
The calibration curve must be known at this point and found to be non-
linear. This calibration can be done using known samples.
The curve has been studied, and breakpoint positions determined on
the most curved portions of the curve. Appropriate breakpoint resistors
have been installed.
1. Remove the shorting jumper previously installed for
nulling steps.
2. Connect a DC voltage source to the input of AlA (pin 3)
and ground. (The DVM is still connected to pin 7 of
A3B.)
3. Apply 0 volts to the input, (V
in
). The output, (V
out
) must
read 0 volts as well.
4. Make V
in
= V
test
(1) per chart. This is the first breakpoint
voltage. NOTE: V
in
must always be positive. Adjust P1
until V
out
= V
lin
(1) per chart. NOTE: make sure P1
changes V
out
.