Fieldpiece ATRMS3 True RMS Converter.

The ATRMS3 converts an “average sensing meter to a true RMS meter. It converts AC voltage to a DC voltage proportional to the true RMS value. When used with a current clamp, it can measure true RMS AC current.

Range settings
The meter should be set to a mVDC range. A “1.0” on the display means 1mVDC. The ATRMS3 switch must be set to correspond to the maximum VAC being input. The 200VAC range should be used for voltages up to 200VAC, the 600VAC should be used for voltages up to 600VAC. The current clamp switch position is used for input voltages up to 200mVAC. (The current clamp converts current going through the jaws to a AC voltage at the rate of 1A/1mVAC.)

Interpreting the display
With the meter set on the mVDC range and the ATRMS3 set on 200VAC, “1.0” on the meter means 1VAC True RMS. For the current clamp, “1.0” means 1AAC. On the 600VAC position, “1.0” on the meter means 10VAC. For example, “44.1” displayed on the meter means 441VAC.