converting analog voltage module to current module
- Thread starter kamalice
- Start date
Steve Bailey
Lifetime Supporting Member + Moderator
Your post isn't clear whether you are talking about an analog input module or an analog output module.
If it is an analog voltage input module and you have a 4 - 20 mA signal, using Ohm's law for the calculation shows that a 4 mA current through a 250 ohm resistor produces a 1 volt potential (voltage) difference across the resistor. A 20 mA current through the same resistor produces a 5 volt potential difference. Since most analog voltage input modules are set up for 1 0 - 10 volt range, the 250 ohm resistor only uses half of the available resolution of the module.
If the 4 - 20 ma transmitter can support the burden, use a 500 ohm resistor to give you a 2 - 8 volt range.
If it is an analog voltage input module and you have a 4 - 20 mA signal, using Ohm's law for the calculation shows that a 4 mA current through a 250 ohm resistor produces a 1 volt potential (voltage) difference across the resistor. A 20 mA current through the same resistor produces a 5 volt potential difference. Since most analog voltage input modules are set up for 1 0 - 10 volt range, the 250 ohm resistor only uses half of the available resolution of the module.
If the 4 - 20 ma transmitter can support the burden, use a 500 ohm resistor to give you a 2 - 8 volt range.
thanks for ur reply. i mention analog input module only
Most 4-20mA driver circuits can suffer the burden, since {most} are designed to be able to drive the current through more than one (sometimes 3 or 4) "receivers", eg. a PLC analog input and an in-line meter, or chart recorder. The specs for the particular device must be checked.
And 4-20mA through a 500 ohm load gives you 2 - 10V, not 2 - 8V.
daba is right for a 4-20mA device connected to a 0-10v input with a 500ohms, you just need to scale it by first substracting the 2volts = to 4ma for broken wires....
but converting a 0-10v signal from a device to connect to a 0-20mA card isn't good with resistors because the reading would change with wire lenght and connection tightening. I could work if it is for an home project or class for 1 time show but in the industry you must use a converter to avoid serious troubles
You would need to take into account wire
but converting a 0-10v signal from a device to connect to a 0-20mA card isn't good with resistors because the reading would change with wire lenght and connection tightening. I could work if it is for an home project or class for 1 time show but in the industry you must use a converter to avoid serious troubles
You would need to take into account wire
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