What resistor value is needed for a 4-20 mA flow transmitter output to match a 1-5 VDC input?

To achieve a compatible relationship between a 4-20 mA output from a flow transmitter and a 1-5 VDC required input, one must consider how to convert the current output into a voltage that meets the specifications.

The output of 4-20 mA is a current signal where 4 mA represents the minimum flow condition and 20 mA represents the maximum flow condition. The goal is to create a voltage across a resistor using Ohm's Law, which states that Voltage (V) = Current (I) × Resistance (R).

Start with the two extreme current levels:

• For 4 mA:

[

V = I \times R = 0.004 , \text{A} \times R

]

• For 20 mA:

[

V = 0.020 , \text{A} \times R

]

To ensure that the output ranges from 1 V to 5 V, we need to set up the following equations:

• When the current is at its minimum:

[

0.004 , \text{A} \times R = 1 , \text{V