Fact:
The specification for the GRV-IVI-12 shows 0.1% of range accuracy.
Background:
I have channel 1 of a GRV-IVI-12 configured for ±1.25V (which should provide ±1.25mV accuracy) as I am measuring the voltage across a shunt that will range from 0-60mV representing 0-10 amps. I was expecting the accuracy to be within 0.42 amps (±0.21A) based on the specification (2.5mV/60mV = 4.167% => 10.0amps * 4.167% = 0.4167 amps). I would have used the GRV-ITMI-8 module for this, but I also needed to measure values at 10V depending on what model equipment is connected (the feedback could be 0-10VDC or 0-60mV).
Issue:
I’m testing this newly built panel and I am seeing a much wider variation in the amp readings on the 0-60mV shunt then the specifications would suggest (a 1.0 amp variance). To rule out an issue with the field equipment or field wiring, I disconnected the wiring from the module and installed a jumper on channel 1. I scaled the channel to read in mV and cleared the min and max values to see what kind of variation I am getting on this channel:
So instead of getting ±1.25mV, I’m seeing ±3mV. This was over a short period of time, about 10 minutes.
Interestingly, changing the module configuration to ±10V, and scaling it to mV, I am seeing the same 6mV variance as ±1.25V. There doesn’t seem to be any improvement in accuracy going from ±10 to ±1.25 as the specifications state. So at 10V, accuracy is well within spec (±10mV), but at 1.25V, it is not.
Is there something wrong with this module, the specification wrong or am I understanding something wrong? I don’t think the 1.0A variation is going to be acceptable to my customer, so I am looking for a good solution here.
*Update - this may be a hardware issue - as it seems to be only this channel behaving that way that I have found so far.
