268XA
Service Manual
2-46
Table 2-18. A/D Reading to Average to Obtain a Reference Balance Measurement
Instrument
Reading Rate Fast
Reading Rate Medium
Reading Rate Slow
PAI
1
5 (60 Hz)
6 (50 Hz)
45 (60 Hz)
48 (50 Hz)
FAI
1
1
5 (60 Hz)
6 (50 Hz)
There are two reference balance readings: one with both references on, and one with both
references off. These readings are intended to compensate for unequal voltage references
in the A/D. They are used to obtain a scale factor, which is then applied to the P counter
for normal measurements.
The scale factor is derived as follows:
S = 1 - {[(16P2 - N2) - (16P0 - N0)]K2}
where
S = scale factor
P2 = P counts (both references on)
N2 = N counts (both references on)
P0 = P counts (both references off)
N0 = N counts (both references off)
K2 = (0.1) / (16) / (1843) / (1.6)
Zero Offset Readings
There are four zero readings: one for each gain setting of the DC buffer amplifier. Zero
offset readings are similar to V dc readings, except that no channel selection is required
and no function relay switching is required. The Stallion chip must be configured. The
A/D is placed in normal measurement mode. The number of readings to average is the
same as for a normal reading (see Table 2-18, A/D Readings to Average to Obtain a
Measurement). Zero offset measurements are converted to volts in the same way as
normal channel measurements, except, of course, that no zero offset is subtracted. The
reference balance scale factor is used.
Housekeeping Schedule
Housekeeping readings are always taken in response to a “Do Housekeeping” command
from the outguard, as described in “Do Housekeeping” earlier in this chapter.
Setting the HK bit in a configuration command causes the inguard to schedule
housekeeping readings on a rotating basis, taking one at the end of each channel scan. It
also enables a timer, which is started at the end of a scan or after a configuration
command. Whenever the timer expires, the next housekeeping reading in the schedule is
measured, and the timer is restarted. The timer is set to expire after 17.476 seconds.
On the medium and slow rate, all six housekeeping readings are scheduled as described
in the preceding paragraph. On the fast rate, however, only zero offset readings are
scheduled. This is because a single reference balance reading is longer than a normal
reading on the fast rate, which would cause scans containing them to take longer.
Summary of Contents for 2680A
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Page 204: ...268XA Service Manual 7 10 268X FINAL ASSEMBLY alg105f eps Figure 7 1 268XA Final Assembly ...
Page 207: ...Replaceable Parts Parts Lists 7 7 13 2680A DIO alg100f eps Figure 7 3 DIO Module ...
Page 209: ...Replaceable Parts Parts Lists 7 7 15 2680A FAI alg102f eps Figure 7 4 FAI Module ...
Page 211: ...Replaceable Parts Parts Lists 7 7 17 2680A PAI alg103f eps Figure 7 5 PAI Module ...
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Page 215: ...8 3 8 Schematic Diagrams Figure 8 1 Backplane PCA 2680A 4001 ...
Page 216: ...268XA Service Manual 8 4 Figure 8 1 Backplane PCA cont 2680A 1001 ...
Page 217: ...8 5 8 Schematic Diagrams Figure 8 2 Controller System Power PCA 2680A 4004 ...
Page 223: ...8 11 8 Schematic Diagrams Figure 8 3 Digital I O PCA 2680A 4006 ...
Page 224: ...268XA Service Manual 8 12 Figure 8 3 Digital I O PCA cont 2680A 1006 1 of 3 ...
Page 225: ...8 13 8 Schematic Diagrams Figure 8 3 Digital I O PCA cont 2680A 1006 2 of 3 ...
Page 226: ...268XA Service Manual 8 14 Figure 8 3 Digital I O PCA cont 2680A 1006 3 of 3 ...
Page 227: ...8 15 8 Schematic Diagrams Figure 8 4 Backplane Extender PCA 2680A 4009 ...
Page 228: ...268XA Service Manual 8 16 Figure 8 4 Backplane Extender PCA cont 2680A 1009 ...
Page 229: ...8 17 8 Schematic Diagrams Figure 8 5 Extender PCA 2680A 4010 ...
Page 230: ...268XA Service Manual 8 18 Figure 8 5 Extender PCA cont 2680A 3010 ...
Page 231: ...8 19 8 Schematic Diagrams Figure 8 6 A D Supply Assembly 2680A 4031 ...
Page 232: ...268XA Service Manual 8 20 Figure 8 6 A D Supply Assembly cont 2680 1031 ...
Page 233: ...8 21 8 Schematic Diagrams Figure 8 7 PCMCIA PCA 2680A 4041 ...
Page 234: ...268XA Service Manual 8 22 Figure 8 7 PCMCIA PCA cont 2686 1041 ...
Page 235: ...8 23 8 Schematic Diagrams Figure 8 8 Output PCA 2680A 4062 ...
Page 236: ...268XA Service Manual 8 24 Figure 8 8 Output PCA cont 2680A 1062 ...
Page 237: ...8 25 8 Schematic Diagrams Figure 8 9 A D PFE PCA 2640A 4003 ...
Page 238: ...268XA Service Manual 8 26 Figure 8 9 A D PFE PCA cont 1 of 6 ...
Page 239: ...8 27 8 Schematic Diagrams Figure 8 9 A D PFE PCA cont 2 of 6 ...
Page 240: ...268XA Service Manual 8 28 Figure 8 9 A D PFE PCA cont 2640A 1003 3 of 6 ...
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Page 244: ...268XA Service Manual 8 32 Figure 8 10 A D FFE PCA 2645A 4003 ...
Page 245: ...8 33 8 Schematic Diagrams Figure 8 10 A D FFE PCA cont 2645A 1003 1 of 6 ...
Page 246: ...268XA Service Manual 8 34 Figure 8 10 A D FFE PCA cont 2645A 1003 2 of 6 ...
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Page 250: ...268XA Service Manual 8 38 Figure 8 10 A D FFE PCA cont 700p29_topress zip 2645A 1003 6 of 6 ...
Page 251: ...8 39 8 Schematic Diagrams Figure 8 11 Analog Input Connector PCA 2620A 4004A ...
Page 252: ...268XA Service Manual 8 40 2620A 1004 Figure 8 11 Analog Input Connector PCA cont ...
Page 253: ...8 41 8 Schematic Diagrams Figure 8 12 Display PCA 1 of 1 ...
Page 254: ...268XA Service Manual 8 42 Figure 8 12 Display PCA cont 1 of 1 ...