4-20 mA spec

[philly]

A spec sheet for a transmitter has the following output data:

"4-20mA = 800ohm max, 12-Bit resolution, internal or external power"

Is this 800ohms refering to the input impedence with the transmitter will be connected to. In this case a PLC input?

Does the internal/external power mean this transmitter can be powered with a 24V loop power or an external power source?

 

[GeorgeB]

A spec sheet for a transmitter has the following output data:

"4-20mA = 800ohm max, 12-Bit resolution, internal or external power"

Is this 800ohms referring to the input impedance with the transmitter will be connected to. In this case a PLC input?

Does the internal/external power mean this transmitter can be powered with a 24V loop power or an external power source?

The 800 ohm is the total loop resistance maximum ... it is not unusual to have more than 1 "load" in the loop ... and the wire resistance. 20 mA through 800 ohms will be 16 volts drop across the loop. NORMALLY this would also include a maximum loop voltage, but here they probably are saying that 24V loop supply and 800 ohm load will allow 8V for the device. I've not seen any PLC with an input impedance higher than 250 ohms, although I have used higher for special requirements ... is the 800 a problem for you?

 

[philly]

The 800 ohm is the total loop resistance maximum ... it is not unusual to have more than 1 "load" in the loop ... and the wire resistance. 20 mA through 800 ohms will be 16 volts drop across the loop. NORMALLY this would also include a maximum loop voltage, but here they probably are saying that 24V loop supply and 800 ohm load will allow 8V for the device. I've not seen any PLC with an input impedance higher than 250 ohms, although I have used higher for special requirements ... is the 800 a problem for you?

I get it. This is the total loop impedence. This makes sense. The spec sheet actually says the device is 7V so you were close. I see now how this all adds to 24V.


Thanks for the help.