Campbell CDM-A100 Series, Instruction Manual

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CDM-A100 Series
26
See Appendix C , Calculating Network Restrictions
(p. C-1)
, for complete
examples.
8.2.1 Measurement Speed
Use the equations in TABLE 8-1 to ensure that the CDM-A100 is able to make
measurements at the speed required. Compare that speed with the scan rate
options for the datalogger to determine if the CDM-A100 measurements can be
done within the main scan or if they need to be performed in a sub-scan or
burst. The Sample Rate refers to the rate at which the CDM-A100 makes
measurements when the Reps parameter is greater than 1.
These equations show that smaller notch frequencies increase measurement
time. At the same time, larger notch frequencies result in lower measurement
resolution. Consider this trade-off when designing your system.
TABLE 8-1. Multiplexed Analog Voltage Measurement Speed
1,2,3
Without Input
or Excitation
Reversal
Measurement
Time (µs)
repetitions
• �𝑇𝑇
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
+
10
6
µs
/s
𝑓𝑓
𝑁𝑁1
+ 184
µs
� + 31
µs
Sample Rate (Hz)
10
6
• �𝑇𝑇
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
+
10
6
µs
/s
𝑓𝑓
𝑁𝑁1
+ 184
µs
�
−1
With Input or
Excitation
Reversal
Measurement
Time (µs)
repetitions
• � 2 • �𝑇𝑇
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
+
10
6
µs
/s
𝑓𝑓
𝑁𝑁1
+ 180
µs
� + 5
µs
� + 31
µs
Sample Rate (Hz)
10
6
• � 2 • ( 𝑇𝑇
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
+
10
6
µs
/s
𝑓𝑓
𝑁𝑁1
+ 180
µs
) + 5
µs
�
−1
With Input
and Excitation
Reversal
Measurement
Time (µs)
repetitions
• � 4 • �𝑇𝑇
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
+
10
6
µs
/s
𝑓𝑓
𝑁𝑁1
+ 180
µs
� + 8
µs
� + 31
µs
Sample Rate (Hz)
10
6
• � 4 • ( 𝑇𝑇
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
+
10
6
µs
/s
𝑓𝑓
𝑁𝑁1
+ 180
µs
) + 8
µs
�
−1
Burst
Measurement
Measurement
Time (µs)
repetitions
•
10
6
µs
/s
𝑓𝑓
𝑁𝑁1
+ 𝑇𝑇
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
+ 215
µs
Sample Rate (Hz)
𝑓𝑓
𝑁𝑁1
1
If the instruction uses excitation, calculate the measurement time separately and add 46 µs for each excitation terminal
used. Refer to Example 3 in Appendix C , Calculating Network Restrictions
(p. C-1)
.
2
Refers to multiplexing circuitry internal to the CDM-A100 series.
3
Default settling time, T
settle
, is 500 µs, minimum 100 µs.
The CDM-A100 auto-calibrates to compensate for changes caused
by changing temperature and aging. This calibration occurs during
downtime for the measurement hardware. A time-consuming
program may prevent background calibration if there is
insufficient downtime.
NOTE