Campbell CDM-A100 Series, Instruction Manual

Page: 35 / 61

CDM-A100 Series
24
8. Operation
The CDM-A100 makes analog measurements under the direction of the
datalogger. Upon compiling the program, the datalogger sends information to
each CDM-A100 about every relevant sequence, scan, and measurement. The
datalogger uses a data sync to initiate measurements on the CDM-A100.
Because measurements can be made in multiple scans, slow sequences, sub-
scans, and subroutines, the datalogger firsts sends a message to the modules
indicating which scan’s measurements are to be made upon the next data sync.
When the CDM-A100 receives a sync signal, it begins making measurements.
The measurement order on the CDM-A100 follows the sequence of the
instructions addressed to it within the current active scan of the datalogger
program. After the measurements are completed, it sends the data to the
datalogger for processing.
8.1 Measurements
Because the CDM-A100 series make measurements similar to the CR6 series
datalogger, refer to the
CR6 Measurement and Control System manual for in-
depth measurement details. Information specific to the CDM-A100 series is
provided in the subsequent sections.
8.1.1 First Notch Frequency
The first notch frequency (f
N1
) determines the lowest frequency that will be
eliminated, or notched out, by a sinc filter. This filter notches out frequencies at
integer multiples of f
N1
by averaging for a time equal to 1/ f
N1
. Thus, lower first
notch frequencies result in longer measurement times. Any value between 2.5
Hz and 30 kHz can be entered, but the value will be rounded to the closest of
16 frequency options, with the midway point rounding up. The options for the
first notch frequency are shown in TABLE
6-2 , Analog Voltage Measurement
Speed
(p. 13)
.
Common options for filtering noise are:
•
30000 – Performs a 0.0333 millisecond integration (for fast
measurements)
•
60 – Performs a 16.67 millisecond integration (filters 60 Hz noise)
•
50 – Performs a 20 millisecond integration (filters 50 Hz noise)
8.1.2 Panel Temperature
Each terminal strip has a panel temperature thermistor (Measurement
Specialties 10K3A1A) located just under its center-point. The CDM-A108
includes two panel-temperature thermistors, and the CDM-A116 includes four.
The thermistor has an interchangeability specification of 0.1 °C for
temperatures between 0 and 70 °C. Below freezing and at higher temperatures,
this specification is degraded. Combined with possible errors in the
completion-resistor measurement and the Steinhart and Hart equation used to
calculate the temperature from resistance, the accuracy of panel temperature is
estimated at ±0.1 °C over 0 to 40 °C, ±0.3 °C from –25 to 50 °C, and ±0.8 °C
from –55 to 85 °C.