m. For greatest measurement accuracy, to eliminate the effects of DC reversal

error in the thermocouple heater, steps i through 1 should be repeated with the

opposite polarity of DC.

Use the average of the two DC voltages, corrected for

AC/DC transfer errors, to determine the RMS AC voltage.

n. Reduce the level of the DC source to its lowest level.

o. Disconnect the input of the Model 1395 from the DC source.

This completes

the measurement procedure.

Figure 2-14.

AC voltage measurement

Learning Event 3:

DESCRIBE THE MODEL B7842 THERMAL CONVERTER

1. The second set of thermal converters used at the secondary level is the Model

B7842 (fig 2-15) which consists of the B7842-1, B7842-2, and the B7842-3.

These

thermal converters have a good frequency response from 5 Hz to 100 MHz.

The

maximum input voltage depends on the model; the B7842-1 has an input of 3 Vrms, the

B7842-2 is 1 Vrms and the B7842-3 is 0.45 Vrms.

The DC output voltage for full

scale input to any of the three is a nominal 7.5 mV with an output impedance of

less than 10 ohms. The input impedance is 50 ohms 0.15 ohm to 10 MHz and the AC-

DC error is 6 percent to 10 MHz.

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