Campbell Scientific CURS100 100 Ohm Current Shunt Terminal Input Module - Manual (Page 9)

CURS100 100 Ohm Current Shunt Terminal Input Module
3.1 Differential Measurement
The voltage across the completion resistor is measured with the differential
voltage measurement. Use VoltDiff() for the CRBasic dataloggers (for
example, CR1000, CR5000, or CR9000(X)). Use Instruction 2 for Edlog
dataloggers (for example, CR10X). The differential voltage measurement
measures the difference in voltage between the low and high terminals. The
CURS100 connects the resistor between the high and the low terminals.
3.2 Completing the Current Loop Circuit
As shown in FIGURE 2-1, the 100 Ω sense resistor in the CURS100 is not
connected to the adjacent ground pin that connects into the datalogger signal
ground (
or AG). Hence, an additional connection must be made in order to
complete the loop, which is commonly done by connecting the CURS100 L
terminal to a datalogger G (power ground) terminal with a jumper wire
(FIGURE 3-1). Connecting the L terminal to the adjacent ground ( or G)
terminal on the CURS100 will result in unwanted return currents flowing into
the datalogger signal ground (
or AG), which could induce undesirable
offset errors in low-level, single-ended measurements. The ground ( or G)
terminal on the CURS100 can be used to connect cable shields to ground.
Completing the loop by connecting voltages other than ground is possible as
long as the datalogger voltage input limits are not exceeded. These input limits
specify the voltage range, relative to datalogger ground, which both H and L
input voltages must be within in order to be processed correctly by the
datalogger. The input limits are ±2.5 V for the CR10(X) and ±5 V for the
CR800, CR850, CR1000, CR3000, CR5000, and CR9000(X). Hence, when
measuring currents up to 50 mA with the CURS100, a connection to datalogger
ground is necessary in order for the resulting (50 mA)
× (100 Ω) =
5 V signal to comply with the ±5 V input limits for the CR800, CR850,
CR1000, CR3000, CR5000, and CR9000(X) dataloggers.
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