MODBUS Variable Span

W

Thread Starter

wangzhichao

Hello,

I feel some confusion about the span of the variable thru MODBUS communication, unlike the Hardware transmission, the 4~20mA of the output of the transmitter shall match to the DCS channel range, i.e., if the output range of the temperature transmitter is 4~20mA matching to 0~100 degree C, the span in the DCS channel should be 0~100 degree C accordingly.

But for the MODBUS communication, is there any problem if the span in the Master (DCS) is 0~500 degree C or 0~50 degree C, if the span of the temperature transmitter still ranges from 0~100 degree C with other parameters (such as pressure, flow, etc.) thru the MODBUS data package.

My understanding is that there will be no problem if the range in the Master for that register can cover the range from the Slave. But the span in the Mater cannot cover, it will cause the over-range data with bad quality. Does my understanding correct?

Thanks,
Wang Zhichao
 
You understand the situation properly.

A 100 Deg C value will 'fit' into a scale 0-500 Deg C, but will not fit into a scale of 0-50 Deg C. If the value is outside the range of the scale for that point, it is handled however the HMI/DCS/SCADA handles out-of-range range data.
 
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