Current-loop measurements

Terminals SE1 and SE2 can be configured to make analog current measurements using the CurrentSE() instruction. Current is measured across the 100 Ω resistor with 140 Ω total resistance to ground. The following image shows a simplified schematic of a current measurement.

Use a CURS100 terminal input module when an application needs more than 2 current inputs or measurements. For detailed instructions, see http://www.campbellsci.com/curs100 .

Voltage ranges for current measurements

The data logger 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 transmitter. This results in the best measurement accuracy The degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard. and resolution The smallest interval measurable..

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.

Example current-loop measurement connections

The following table shows example schematics for connecting typical current sensors and devices. See also Current-loop measurement specifications.

Sensor type	Connection example
2-wire transmitter using data logger power
2-wire transmitter using external power
3-wire transmitter using data logger power
3-wire transmitter using external power
4-wire transmitter using data logger power
4-wire transmitter using external power