Figure 2-4. Model 540B block diagram

DC Low Frequency Thermal Measurments
Page Navigation
25

(5) When the Model 540B is operated in the SHUNT mode, no protection is

provided for either the Model 540B thermocouple or for the current shunt.

It is

necessary to exercise caution when operating in this mode to prevent damage to the

instrument.

Figure 2-4.

Model 540B block diagram

i. Figure 2-5 is a simplified representation of the search circuit.

Attenuator components shown are those selected when the range switch is in the I-V

position.

The search circuit is composed of three basic elements; the search-

compensated attenuator, search amplifier, and percent input meter.

(1) The search-compensated attenuator is compensated to equalize the output

of the search amplifier in order to give the percent input reading a favorable

(2) The search amplifier is a two-stage transistor amplifier composed of

Q301 and Q302 and the associated parts. Low frequency adjustment and calibration

is accomplished with R310. High frequencies are calibrated with C305. CR301 and

CR302 rectify the amplified AC and capacitors C303 and C304 filter the resultant DC

voltage for application to the PERCENT INPUT meter.

The search amplifier is not

used in DC SEARCH and a path is provided by the MODE switch to apply DC directly to

the meter from the attenuator.