Campbell CDM-A100 Series, Instruction Manual

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CDM-A100 Series
10
5.1.1.2 Differential Measurements
A differential measurement measures the difference in voltage between two
input terminals. Use a differential measurement to measure current by using
external resistors to convert current to voltage. The CDM-A108 has 8 H/L
differential terminals, and the CDM-A116 has 16.
5.1.1.3 Period-Averaging
Single-ended terminals on the CDM-A108 and CDM-A116 are also
configurable for measuring the period of an analog signal.
•
Voltage gain: 1, 3.8, 19, 67
•
Maximum frequency: 200 kHz
•
Resolution: 130 ns ÷ number of cycles to be measured
5.1.2 Voltage and Current Excitation
X terminals supply switched voltage or current to sensors. The CDM-A108 has
two X terminals, and the CDM-A116 has four.
•
Voltage Excitation (switched-analog output) – X terminals,
configured for voltage excitation output, supply precise voltage in the
range of ±5000 mV. These terminals are regularly used with resistive-
bridge measurements. Each terminal will source up to ±50 mA.
•
Current Excitation (switched-analog output) – X terminals, configured
for current excitation output, supply precise current in the range of
±2.5 mA. These terminals are regularly used with resistive-bridge
measurements.
5.1.3 Switched Voltage Output
SW5V and SW12V terminals supply voltage and control for sensors. The
CDM-A108 includes two SW5V and one SW12V terminals. The CDM-A116
includes four SW5V and two SW12V terminals.
•
5 V control – SW5V terminals supply 5000 mV. See Section 6.5.3 ,
Switched 5 Vdc
(p. 16)
, for information on voltage and current sourcing
limits.
•
Switched 12 V – SW12V terminals supply 12 V and will source up to
200 mA each.
5.1.4 Grounding Terminals
Proper grounding lends stability and protection to a data acquisition system. It
is the easiest and least expensive insurance against data loss — and often the
most neglected. The following terminals are provided for connection of sensor
and CDM-A100 grounds:
•
Signal Ground (
⏚
) – reference for single-ended analog inputs,
excitation returns, and as a ground for sensor shield wires. Current
loop sensors, however, should be grounded to power ground.
•
Power Ground (G) – return for 5V, 12V, and current loop sensors. Use
of G grounds for these outputs minimizes potentially large current
flow through the analog-voltage-measurement section of the wiring
panel, which can cause single-ended voltage measurement errors.