Converting mA to Voltage Signals
Converting mA to voltage is common in HVAC when working with pressure transducers. Terminology to keep in mind includes:
1 mA = 0.001 AMP (short for amperes)
Amps are referred to as CURRENT
Resistor values are in OHMS (Ω is the symbol for ohms)
VOLTAGE is the result of passing amps through a resistor
In order to change mA (current) to voltage, you need to pass the current through a resistor.
The formula for voltage is:
E = IR
E stands for volts, I stands for amps, and R stands for resistance
In control circuits, the most common resistor values are 250Ω & 500Ω, although any value can be used depending upon the device.
If your control circuit is using a 250Ω resistor: | ||
mA | Amps x Resistance | Volts |
4 | 0.004 x 250Ω | 1 |
5 | 0.005 x 250Ω | 1.25 |
6 | 0.006 x 250Ω | 1.5 |
7 | 0.007 x 250Ω | 1.75 |
8 | 0.008 x 250Ω | 2.0 |
9 | 0.009 x 250Ω | 2.25 |
10 | 0.010 x 250Ω | 2.5 |
11 | 0.011 x 250Ω | 2.75 |
12 | 0.012 x 250Ω | 3.0 |
13 | 0.013 x 250Ω | 3.25 |
14 | 0.014 x 250Ω | 3.5 |
15 | 0.015 x 250Ω | 3.75 |
16 | 0.016 x 250Ω | 4 |
17 | 0.017 x 250Ω | 4.25 |
18 | 0.018 X 250Ω | 4.5 |
19 | 0.019 x 250Ω | 4.75 |
20 | 0.020 x 250Ω | 5 |
If your control circuit is using a 500Ω resistor: | ||
mA | Amps x Resistance | Volts |
4 | 0.004 x 500Ω | 2 |
5 | 0.005 x 500Ω | 2.5 |
6 | 0.006 x 500Ω | 3 |
7 | 0.007 x 500Ω | 3.5 |
8 | 0.008 x 500Ω | 4 |
9 | 0.009 x 500Ω | 4.5 |
10 | 0.010 x 500Ω | 5 |
11 | 0.011 x 500Ω | 5.5 |
12 | 0.012 x 500Ω | 6 |
13 | 0.013 x 500Ω | 6.5 |
14 | 0.014 x 500Ω | 7 |
15 | 0.015 x 500Ω | 7.5 |
16 | 0.016 x 500Ω | 8 |
17 | 0.017 x 500Ω | 8.5 |
18 | 0.018 x 500Ω | 9 |
19 | 0.019 X 500Ω | 9.5 |
20 | 0.020 x 500Ω | 10 |