Current to Voltage converters or I to V converters as they are generally known are popular in process control applications where we need to interface output from transmitters to a data-acquisition system. Transmitter output are generally in 4 to 20 mA format which has to be converted to voltage form before feeding to a DAQ device.
In this post I will discuss about different circuits which convert 4-20 mA signals to 1-5V, 0-5V, 1-10 V and 0-10V form.
- 4-20mA to 1-5VDC
The first circuit is a simple implementation of I-V converter. The value of resistor R is 250Ohm.
For 4 mA current, the voltage drop is 4*250 = 1V,
For 20 mA current, the voltage drop is 20*250 = 5V.
This circuit can load the current source (transmitter output DAC) when DAQ device or measuring meter is connected across the resistor causing error in measurement. By adding a buffer/ voltage follower, we are adding very input impedance across the resistor. This protects the source from getting loaded and provide accurate measurement of voltage drop.
One very common configuration of I-V converter using Op-amp is as below. The load is floated in this case.
At the output stage, inverting op-amp is used to get 1-5Volt.
- 4-20 mA to 0-5 VDC
Just by changing the resistor value to 312.5 Ohm and adding an adder circuit with -1.25 V offset voltage, we can convert 4-20 mA to 0-5 VDC. The schematic is shown below.
- 4-20 mA to 0-10 VDC
The circuit is same as above, only the value of resistor is changed to 625 Ohm and offset voltage is set to -2.5 VDC.
There is one more way of getting 0-10V. Here we will use 0-5VDC circuit with slight modifications. The op-amp is used in non-inverting configuration to provide a gain of 2.
- 4-20 mA to 1-10 VDC
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