Voltage Ranges For Current Measurements; Ma And 4-20 Ma Measurements; Cr300 Current Measurement; Ma And 4-20 Ma Sensor Example Connections - Campbell CR300 Series Operator's Manual

ground (⏚) closest to the terminal used. FIGURE
schematic of a current measurement.
FIGURE 6-1. CR300 Current Measurement

6.1.3.1 Voltage Ranges for Current Measurements

The CR300 measures the current through the use of a 100 Ω resistor. Thus, like
a single-ended voltage instruction, it requires a voltage range option. In
general, use the smallest fixed-input range that accommodates the full-scale
output of the transducer. This results in the best measurement accuracy and
resolution. The CR300 has two fixed input voltage ranges: –100 to +2500 mV,
and –34 to +34 mV.
To select the appropriate voltage range, the expected current output range must
be known. Using Ohm's Law, multiply the maximum expected current by 100
Ω to find the maximum voltage to be measured. Because the maximum voltage
input is 2500 mV, the maximum current input must be 25 mA or less.
An approximate 10% overhead on voltage input ranges reduces the chance of
overrange. For example, overrange on the –100 to +2500 mV input range
occurs at approximately –110 mV and 2750 mV. The CR300 indicates a
measurement overrange by returning a NAN for the measurement.

6.1.3.2 0-20 mA and 4-20 mA Measurements

TABLE
4 – 20 mA sensors and devices.
6-2 shows example schematics for connecting typical 0 – 20 mA and
TABLE 6-2. 0–20 mA and 4–20 mA Sensor Example Connections
2-wire transducer using
datalogger power
CR300-Series Datalogger
6-1 shows a simplified
31