Fluke 2680A, Руководство по обслуживанию

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Theory of Operation
A/D Theory of Operations
2
2-19
Channel Selection Circuitry
Channel selection is done using reed relays on the PAI and by optically coupled
solid-state relay on the FAI. Channel selection is done by a set of 24 relays organized in a
tree structure. Relays A3K1 through K20 select the specific channel 1-20. The selection
of relays A3K21 through K24 (Treeing Relays) depends on which bank of 10 channels is
being used (both banks are selected for four-wire ohms) and the channel function and
range being used.
DC Volts and Thermocouples Measurement Circuitry
For 3 V and lower ranges, the input to Stallion (A3U30) are as follows for signal HI and
signal LO inputs:
•
HI is a direct input via the HI SENSE line A3R111, A3K26, A3R130, and pin 50
(HI1) input of A3U30.
•
LO is an input to LO SENSE via A3R132 to pin 80 (LO2) of A3U30.
For the 30 and 300 volt range, the input to Stallion (A3U30) are as follows for the HI and
LO signal inputs:
•
The HI signal is scaled by A3Z7. The input is applied to pin 1 of A3Z7 and a 101:1
divider is formed by the 10 M
Ω
100 k
Ω
resistors when switches S3 and S13 are
closed. The attenuated HI input is then sent via S24, S64, and S44 to the Buffer
Amplifier and then to A/D Converter.
•
The LO signal is sensed through A3L52, A3R146, A3K27, A3R119, and S33 and
S37.
The outputs from Stallion (A3U30) are as follows:
•
HI (pin 20) is to Buffer Amplifier circuitry (A3U27 and A3U28).
•
LO (pin 100) is to Buffer Amplifier circuitry (A3U27 and A3U28).
The ranges for the buffer amplifier are shown in Table 2-3 and measurement matrix in
Table 2-4. Figure 2-6 shows a simplified signal path for the 300 V dc range.
Table 2-3. Range of Buffer Amplifier
Range Buffer Range Control Signals (Gain)
90 mV Range BR1 (x32.168 gain)
300 mV Range BR3 (x10 gain)
750 mV Range BR2 (x4.021 gain)
3 V Range BR4 (x1 gain)
30 V Range BR3 (x10 gain)
300 V Range BR4 (x1 gain)