CurrentSE (Single-Ended Current)

The CurrentSE instruction is used to make a single-ended current measurement on the RG terminal. The output is in milliamps.

NOTE: COMPATIBLE ONLY WITH CR6 SERIAL NUMBERS ≥ 7502 CONTAINING BOARD REVISION 19 OR LATER

Syntax

CurrentSE ( Dest, Reps, Range, RGChan, MeasOff, SettlingTime, fN1, Mult, Offset)

Following is a program showing the use of the CurrentSE instruction.

'Declare Variables
Public Cur_SE
DataTable(Hourly,True,-1)
  DataInterval(0,60,Min,0)
  Sample(1,Cur_SE,IEEE4)
  Average(1,Cur_SE,IEEE4,0)
  Minimum(1,Cur_SE,IEEE4,0,0)
  Maximum(1,Cur_SE,IEEE4,0,0)
EndTable

BeginProg
  Scan(1,Sec,1,0)
    'Generic CurrentSE measurement:
    CurrentSE(Cur_SE,1,mv200,RG,True,0,60,1.0,0.0)
    CallTable(Hourly)
  NextScan
EndProg


Remarks

The datalogger has built-in 101 ohm shunt resistors on the RG terminal that allows the datalogger to measure a 4 to 20 mA sensor. The 101 ohm shunt resistance is a 91 ohm resistor in series with a 10 ohm resistor. The instruction measures differentially across the 10 ohm resistor.

The maximum valid measurement range is + 80 mA. For current beyond + 80 mA, protection circuitry will affect the measurement.

The following image shows the typical wiring for a 2-wire transmitter using datalogger power.

Parameters

Dest (Destination)

The Variable in which to store the results of the instruction. Right-click the parameter to display a list of defined variables.

If this instruction has a Repetitions parameter and it is greater than 1, the results are stored in an array with the variable name. The array must be dimensioned large enough to hold all of the values returned from all of the Reps.

Type: Variable or Array

Reps (Repetitions)

The number of repetitions for the measurement or instruction.

Type: Constant integer (or expression that evaluates as a constant).

For the CurrentSE instruction, measurements are made on consecutive channels. If the Reps parameter is greater than 1, the Dest parameter must be a variable array.

Range

The expected input from the sensor. To choose the appropriate range, multiply the expected current by 10 (ohms).

Right-click the parameter to display a list or enter the code directly.

Code Description
mV1000 +1000 mV
mv200 +200 mV
Autorange Datalogger tests for and uses most suitable range

For signals that do not fluctuate too rapidly, AutoRange allows the datalogger to automatically choose the input voltage range. AutoRange results in two voltage measurements being performed. The first voltage measurement is done quickly at a first notch frequency (fN1) of 50 kHz, the result of which determines the input voltage range to use for the second measurement. Autorange should not be used if fast measurements are required or if the analog signal could change significantly over the course of the measurement.

Type: Constant

RGChan (Resistive Ground Channel)

The CR6 has only one RG terminal.

Type: Constant

MeasOff (Measure Offset Voltage)

Determines whether the ground offset voltage is measured before the measurement is made on the analog channel. If the ground offset is measured it is subtracted from the sensor measurement and the result is stored in Dest.

Value Result
0 Offset voltage is corrected from background calibration.
1 Offset voltage is measured each scan (this option effectively increases the measurement time as if an additional rep were added to the instruction).

Type: Constant

Settling Time

The settling time is the duration (in microseconds) to allow for signal settling after setting up a measurement (switching to the channel, setting the excitation) and before making the measurement. Minimum settling time is 20 microseconds; maximum settling time is 600 ms. If 0 is entered, a default of 500 microseconds is used.

Additional settling time may be necessary to allow the signal to settle with high resistance or long lead lengths (higher capacitance). The time it will take to make the measurement will include the measurement itself, the SettlingTime, fN1, and whether or not parameters are set to remove voltage offset errors. Using either RevDiff or RevEx causes two SettlingTimes to occur per channel; four SettlingTimes will occur when using both RevDiff and RevEx.

Type: Constant (or expression that evaluates as a constant)

fN1

Determines the lowest frequency that will be eliminated or notched out by the sinc filter. This filter notches out frequencies at integer multiples of fN1 by averaging for a time equal to 1/fN1; thus, lower fN1 frequencies result in longer measurement times. Set fN1 to the lowest frequency that should be filtered out. For example, setting fN1 to 60 filters all multiples of 60 and above (60, 120, 180, etc.) but will not effectively filter lower frequencies; for example 30 Hz. Any value between 5 Hz and 93.75 kHz can be entered, but common options for filtering noise are:

Option Description
15000 Performs a 0.0667 millisecond integration (for fast measurements)
60 (or _60Hz) Performs a 16.67 millisecond integration (filters 60 Hz noise)
50 (or _50Hz) Performs a 20 millisecond integration (filters 50 Hz noise)

Type: Constant

Mult, Offset (Multiplier and Offset)

Factors by which to scale the raw results of the measurement. Typically used to convert the raw measurement to engineering units or to units other than which is output. For example, the TCDiff instruction measures a thermocouple and outputs temperature in degrees C. A multiplier of 1.8 and an offset of 32 will convert the temperature to degrees F.

For temperature measurements, a multiplier (mult) of 1 and an offset of 0, would output in degrees Celsius. For analog measurements, a multiplier (mult) of 1 and an offset of 0, would output the measured voltage in millivolts divided by the excitation voltage in volts.

If Repetitions of greater than 1 are used for this instruction, Repetitions can also be used for the Multiplier and Offset. See Multipliers, Offsets, and Disable Variables with Repetitions for more information.

Type: Constant, Variable, Array, or Expression

Related Sensors

This instruction is used by the following sensors:

NOTE: This is not an all-inclusive list of sensors that require this instruction. Refer to the owners manual of your device for more specific instructions.