Problem with ABB Commander 1900 series circular chart recorder

I got an issue regarding an ABB Commander 1900 chart recorder..the recorder is connected in series with a controller, a 24 volt DC supply and a transmitter (2 wire RTD, loop powered)..the recorder is used to indicate temperature..the controller when replaced by another PLC, the indicator is showing an error value, somewhat 15 degrees more from what is anticipated..the PLC has an indication too which is showing a room temperature of almost 29 degrees which is also shown correct in the Transmitter local indication too..but the recorder value is still an error..this happened when the controller is replaced by the PLC..is it something related to the internal resistance of the replaced component..pls help..

Dhillis,

Is your PLC Analog Input set up for the proper current loop (instead of voltage)? If it is, then probably your PLC input impedance is not the same as the old controller. Your signal transimitte may not have enough power to handle the new set-up. The PLC input may not be "isolated" completely, so the easiest, surest fix is to buy a signal conditioner that provides terminals for Miliamps IN and Milamps Out (which will be the isolated signal to your PLC.

Lancie1,

Can you tell me how to check the input impedance of those two devices..

The easiest method is to read the specifications for the devices. The specs will include the input impedance or resistance. If your PLC input impedance is much lower than that of the old controller, it will draw more power from your 24 VDC power supply (which may not have enough capacity to handle the additional load).