4-20ma interfacing with 9203 module

[kc64]

I have a client with various 4-20ma senders.  One sender spec states that the load resistance must be >= 250 ohms.  We plan to use the 9203 module, the spec sheet of which states that the input impedance is 138 ohms.  I plan to add a series resistor to the channel to increase the load resistance to >= 250 ohms.  Any thoughts on this approach?

[AnalogKid2DigitalMan]

kc64:

Your approach should work, just don't go with too high of a resistor or you may exceed the compliance voltage that the sender can deliver.

-AK2DM

[acardoso]

Hi,

are you sure, that is the other way around. I you put a resistor of 1kOhm, at 20mA, you will 20V. With a load loop resistor of 250Ohm, you get 5V.

Remember this, if you use a LEM to measure current, you will get a load loop resistor of 0Ohm.

Best Regards,

António

[AnalogKid2DigitalMan]

The sending device can output only so many volts, typically a few volts below it's supply voltage.

Say the sender was powered by a 12V supply. If 1Kohm was the loop resistance, there is no way the device could send a 20mA signal since the 20V loop drop exceeds what the sender is being supplied with (12V).

-Ak2DM

[kc64]

Actually, the device is powered by the same two wires that provide the loop current.  There are no other power supply wires.

[sparkymark567]

The requirement for load resistance >250 ohms seems odd to me also, is this the wrong way round?

Should the load resistance be less than 250 ohms.

Does the device have HART communication? What sensor is it?

[alexrn2539]

Hart es diferente a 4- 20 mA