Campbell CDM-A100 Series, Instruction Manual

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CDM-A100 Series
29
8.3 Multiple Devices
Multiple CDMs may be connected to a single datalogger using a daisy-chain or
star topology (see Section
7.6 , Connecting Multiple CDMs
(p. 21)
). In both
network configurations, as total cable length increases, the maximum possible
bit rate decreases. Limitations on cable length and baud rate are examined in
the document
Designing Physical Network Layouts for the CPI Bus , which is
available at www.campbellsci.com/app-notes .
When including two or more CDM-A100 devices in the program, the
processing mode of the datalogger affects the measurement timing of each
CDM-A100. In
sequential mode
, the CDM-A100 devices make measurements
one after the other, following the order of their instructions within the program.
Conversely, in
pipeline mode , the devices start their measurements
simultaneously. Pipeline mode is recommended.
In either mode, measurements that require excitation MUST be
made on the same CDM-A100 that provides the excitation voltage
or current.
8.4 Switched Voltage Output
8.4.1 Switched 5 Vdc
An SW5V terminal is normally used to operate an external relay-driver circuit
because the port itself has limited drive capacity. Drive capacity is determined
by the 5 Vdc supply, a Schottky diode, and a 30 Ω output resistance. It is
expressed as:
V
0
= 5 V – 0.3 V –
(30 Ω) x I
0
Where V
0
is the drive limit, and I
0
is the current required by the external
device. FIGURE 6-1 , Current sourcing on SW5V terminals
(p. 16)
, shows the
relationship between supply voltage and current load.
8.4.2 Switched 12 Vdc
The SW12V terminals are used to power devices such as sensors that require
12 Vdc during measurement. Current sourcing must be limited to 200 mA or
less on each channel. When the supply voltage is below 14.5 Vdc, the voltage
on the SW12V terminals track the power supply. Voltage on these terminals is
regulated to 12.5 ± 0.5 Vdc when the supply voltage is 14.5 to 32 Vdc.
9. Maintenance
•
Protect the CDM-A100 from humidity and moisture.
•
Send to Campbell Scientific for factory calibration every three years.
9.1 Factory Calibration or Repair Procedure
If sending the CDM-A100 to Campbell Scientific for calibration or repair,
consult first with a Campbell Scientific representative. If the CDM-A100 is
malfunctioning, be prepared to perform some troubleshooting procedures while
on the phone with Campbell Scientific. Many problems can be resolved with a
NOTE