Jett

How can I send a value from Dasylab to an external device such as an ESC 8864 data controller via Modbus? I have tried using a simple slider to send data to the external device using the Modbus Analog Output module, but have not been able to make this work. I believe the register that I want to write to is 40,010. I have been able to use the Modbus Analog Input Module, Modbus Digital Input Module and Modbus Digital Output Modules, but not the Modbus Analog Output Module. What could i be missing considering the other modules all work. I have tried many different combinations of Data Types and Registers on the Properties page, but nothing seems to work.

Fausto, We tried both scenarios with no luck. Initially we set up the circuit in accordance with the first figure. In that scenario the plant provided the 24 volt DC but no resistance. In the second scenario we moved pins on the analog input card of the plant DCs so that we could use an external power supply. In this scenario the analog input card provided the 250 ohm resistance. In neither case was the plant DCS able to get an accurate reading. I'm using a laptop. In both instances I could measure the correct current at the input of the analog input card of the dcs. The odd part is that when we simulate or source milliamps into the DCs the DCs reads correctly. Should I be using any type of isolation devices? For instance should I use a USB isolation device and should I use isolators for each current loop? Lastly is there any requirement to use a 250 ohm resistor when the loop is providing the power as in example one in the manuals schematic?

Does anyone know of a reason that would prevent accurate readings on a plant DCS when supplying it with a 4-20mA signal from a USB-3104? We have confirmed that the plant DCS is accurate. We have also confirmed that the mA output from the USB-3104 is accurate, but when the two are connected together the readings are not even in the same ballpark. We're connecting to a Delta V DCS. Thank you, Jett