Campbell Hausfeld 4-Channel Current/Voltage SDM-CVO4 - Manual (Page 19)

Instruction Manual
compensated for. With the SDM-CVO4 as an excitation source, any drift in its
output accuracy, or of the logger measurement accuracy, can result in a
combination of those errors. It is worth investigating, therefore, the exact
requirements of the sensors you wish to use. For instance, on closer inspection of
the specification of many pressure sensors you will often find the recommendation
of 10V excitation, but in reality many will accept a lower voltage. If new sensors
are to be bought for a specific project, it can be worth checking if versions of
sensors are available that will accept a low voltage excitation.
There are, however, some sensors that have active components or that have large
common mode output voltages that require an isolated and/or precise high voltage
supply within the current output capability of the SDM-CVO4. In this context the
SDM-CVO4 can be used to provide an isolated supply which can be regulated in
the range of 0-10,000 mV, a regulated current (0-20 mA) or an unregulated 15 V
(nominal) supply (by setting current output mode and using the V
o
terminal).
In these applications, if all channels of the SDM-CVO4 are being used for
exciting sensors, you can use the standby mode between measurements to save
power. To do this you would send a command (instruction 103 with zero reps -
see below) to the SDM-CVO4 to shut it down after making the measurements.
When using this mode you need to allow at least 100ms after turning the
SDM-CVO4 on again (by using instruction 103 with a non-zero number of reps)
for the outputs to stabilize, before starting your measurement sequence.
It is possible that you can power more than one sensor from each output of the
SDM-CVO4, either by parallel connection in voltage output mode or serial
connection in current output mode. Make sure, however, that you do not try to
take more current than available in voltage mode. Additionally you also need to
check that all outputs from the sensors powered by one channel do not have a
spread which exceeds the common mode range of the datalogger inputs.
6. Datalogger Programming
Our CR10(X), 21X, and CR23X dataloggers use Edlog Instruction 103. Our
CR800, CR1000, CR3000, and CR5000 use the SDM-CVO4 instruction in
CRBasic. Both Edlog and CRBasic are provided in PC400 or LoggerNet
software.
6.1 Edlog Instruction 103
To allow full backwards compatibility with older dataloggers and operating
systems, the SDM-CVO4 is designed to work with the instruction supplied to
control the SDM-AO4 – Instruction 103. However, most datalogger manuals and
program editor help systems do not refer to the SDM-CVO4 in the description of
Instruction 103. Please see the details of use below to understand the differences.
Instruction 103 is described in Table 6-1 and allows you to set four separate
output levels for one SDM-CVO4, or several output levels with multiple
SDM-CVO4s. Output levels are reset each time Instruction 103 is executed.
Instruction 103 was originally designed to take an input location range of
-5000 to +5000 and output this directly in mV when using the SDM-A04. When
used with the SDM-CVO4, the same range of values (±5000) in an input location
is used to scale the output to 0-10000mV for voltage mode, or
0-20 mA for current output mode.
In most applications a specific range of a measured value is scaled to utilize the
full scale output of SDM-CVO4. For instance, a temperature sensor reading in the
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