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Service Manual
2-20
Table 2-4. Analog Measurement Processor Pin Descriptions (cont)
Pin Name Description
46
47
48
49
50
SUM
B.1
B.32
B1
B3.2
Integrator summing node
Buffer output, 100 mV range
Buffer output, 300 mV range
Buffer output, 1000 mV range
Buffer output, 3V range
51
52
53
54
55
VREF+
VREF-
RAO
RA+
RA-
A/D voltage reference plus
A/D voltage reference minus
A/D reference amplifier output
A/D reference amplifier noninverting input
A/D reference amplifier inverting input
56
57
58
59
60
AFO
MOF
AFI
FAI
FAO
Passive filter 2
Passive filter 1 plus resistance
Passive filter 1
Filter amplifier inverting input
Filter amplifier output
61
62
63
64
65
RMSF
AGND3
RMSG
2
RMSO
CAVG
RMS output, filtered
(not used, connected to filtered -5.4V dc)
(not used)
RMS converter output
(not used)
66
67
68
VSSR
RMSG
1
RMSI
-5.4V dc, filtered
(not used, pulled to filtered -5.4V dc)
(not used)
2-52. Input Signal Conditioning
Each input is conditioned and/or scaled to a dc voltage appropriate for measurement by
the a/d converter. DC voltage applied to the a/d converter can be handled on internal
ranges of 0.1V, 0.3V, 1V, or 3V. Therefore, high-voltage dc inputs are scaled, and ohms
inputs are converted to a dc voltage. Line voltage level ac inputs are first scaled and then
converted to a dc voltage. Noise rejection is provided by passive and active filters.
2-53. Function Relays
Latching relays A3K15, A3K16, and A3K17 route the input signal to the proper circuit
blocks to implement the desired measurement function. These relays are switched when
a 6-millisecond pulse is applied to the appropriate reset or set coil by the NPN
Darlington drivers in IC A3U10. The A/D Microcontroller A3U9 controls the relay drive
pulses by setting the outputs of port 6. Since the other end of the relay coil is connected
to the VDDR supply, a magnetic field is generated, causing the relay armature and
contacts to move to (or remain in) the desired position. Function relay states are defined
in Table 2-5.