Figure 1-13. Temperature Indicator Compensator.

Figure 1-12. Typical Display and Counter Board Circuitry.

Figure 1-14. Temperature Indicator Amplifier Circuit.

TM-55-4920-401-13P Test Set Fuel Quantity Gage Capacity Type P/N 361 010 002 Manual
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plays (I’s). Since the CLD’s have no BCD decade counter output; for BCD-DAC decoding, BCD de- cade counters (DC’s) are added to the display and counter board for this purpose. LAMP TEST, gener- ated by the PRESS TO TEST switch, lights all seg- ments in the displays. RESET, from the A/D con- verter, resets the counter-latch-decoders at the beginning of the reference integration period. TRANSFER-TO-MEMORY, from the A/D con- verter, transfers the CLD count into the CLD latches at the conclusion of the reference integra- tion period to update the display. The blanking TM 55-4920-401-13&P input of the CLD’s is controlled by FF2B (fig. 1-3) and goes high to blank an indicator display on every other reading when the input signal to the indicator is out-of-range. (2) Temperature Indicator. The following subparagraphs describe circuitry that is unique to the temperature indicator. ( a ) T e m p e r a t u r e S i g n a l C o n d i- tioning. A thermocouple circuit is formed when the thermocouple wire of the measuring junction is connected to the copper wiring of the A/D converter at the Compensator (fig. 1-13). The junction at the Figure 1-13. Temperature Indicator Compensator. compensator is called the reference junction. Any RT. The negative thermocouple lead is connected variation in the temperature of the reference junc- tion will cause either an increase or decrease in the signal voltage. To measure temperature accurately, the reference junction must either be held at a con- stant temperature or referenced to a voltage which varies with temperature and in relation to the ther- mocouple curve. The compensator generates a refer- ence voltage through the use of a thermal resistor, with copper wire to the higher potential end of this resistor. The thermal resistor, having a positive temperature coefficient, modifies the reference voltage when the ambient temperature increases. To assure that their temperatures are the same, the reference junction and thermal resistor are encapsulated. 1-12

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