Learning Event 3:
DESCRIBE THE MODEL 1600A CIRCUIT
1. The Model 1600A block diagram is shown in Figure 3-6. The ATS consists of 15
major functional circuits interconnected as shown in the block diagram. AC signals
to be measured are applied to one of two AC INPUT connectors, depending on the
signal level, and are coupled to the removable transfer assembly which contains
attenuators, a thermoelement, and an overload protection circuit. Figure 3-7 is a
simplified representation of the input circuitry.
The low and high voltage
attenuators are fixed resistance which are paralleled by changing the range switch
setting to vary their series resistance. This prevents the voltage coupled to the
thermoelement heater from exceeding its maximum voltage rating of approximately
0.45 volts rms.
a. The overload protection circuit is located between the attenuator output
and the thermoelement heater to disconnect the applied signal from the attenuator
should the signal be greater than the measurement range selected by the range volts
switch.
b. The thermoelement, being an RMS device, develops a DC output related to
the RMS value of the attenuated input signal.
Since the thermoelement has a
maximum output level of approximately 7 millivolts, this low-level DC voltage is
chopped and fed to an amplifier.
The use of a chopper/amplifier eliminates the
drift problems normally associated with the measurement of low-level DC voltages.
Figure 3-6.
Model 1600A block diagram
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