Why Doesn't the Theoretical Power Value Match the Measured Power Value?

Check for differences in the specifications or features of the instruments.

For values that do not match when inputting a 50/60 sine wave

• Check whether the value is within the specifications (error) of each power meter.
• Check the DC offset in DC mode
• Check whether the measuring range is set appropriately.
• Check whether your power meters have harmonic measurement functions.

If the measuring range is too large relative to the input signal, the amount of error will increase. Differences in measured values can occur due to DC offset and other effects on AC power meters and AC/DC power meters. If the waveform is subtly distorted, harmonic components are present. The effects of such harmonic components can cause differences in measured values between power meters dedicated for 50/60 Hz and power meters supporting harmonics. 

For values do not match when inputting distorted waves or high frequency waves

• Check whether the value is within the specifications (error) of the high frequency input of each power meter.

If the measured values on power meter A are larger than those from power meter B, there are at least two possibilities:

1. The frequency characteristic (bandwidth) of power meter A is higher (frequencies are attenuated on power meter B).
2. Power meter B has superior common mode (voltage) rejection ratio characteristics.