### Scales

December 14, 2021

#### by Tom Lish

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 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