GP-HR mA Application
Notes
Any combination of the three analogue inputs of the GP-HR Logger can be configured to read milliAmps. A load resister is required between the input line and the common
line. The value of load resister chosen will determine the current range of the input. The
channels must then be setup to milliAmp mode using the OmniLog Software. 1, 2 and 3 input
0 to 20mA adapters are supplies as standard probe sets. These have the correct load
resisters fitted inside the adapter socket. mA1-PS mA2-PS mA3-PS
The Load Resister
Typically for 4 to 20mA sensors a 68ohm 0.1% 25ppm (Farnell
part number 434-887 or 343-935) load resistor is used. This gives the input range of 0 to
30.1mA
If you use the factory default reset to configure a GP-HR
as a 1, 2 or 3 channel milliAmp Logger, the offset and gain for the milliAmp channels will
be set assuming a 68ohm load resistor. This will give an accuracy of ± 3%.
Using manual calibration, an accuracy of ± 0.1% can be
obtained at any given temperature. For operation over the loggers temperature range of
-30° C to 70° C an accuracy of ± 0.3% can be obtained.
To calculate the required resistance for any given current
range use the following formula:
Required resistance in ohms = 2.048 /
max current required in amps
Where low thermal coefficients are required use high
precision resisters. (We recommend at least 0.1% 25ppm )
Example:
- Required current range 0 to 100mA
- Required resistance in ohms = 2.048 / 0.1A = 20.48 ohms
Circuit for GP-HR with 3 current inputs
Setting up mA channels using the
OmniLog Software
Connect the GP-HR logger to a computer and Run the OmniLog
software
From the Logger
Control Screen select Channel and Probe Setup
Select the Channel that you wish to setup (Ch 1, 2 or 3)
From the Probe box select the milliAmp option as shown
Notice that after the milliAmp probe has been chosen the Units in the Unit and
Scaling box has been set to mA and the Gain
will be set to a default value.
Now give the Channel a meaningful Long and Short name in the Logger
Channel Name box as shown below
Click on the Write Unit, Scaling and Calibration values to the Logger button to send the new settings to the logger.
If you wish to calibrate the mA channel at this point,
follow the calibration procedure in the OmniLog Help User Manual. You can see this
procedure by clicking on the Calibration
Notes button in the Calibration
box.
