Low frequency measurement requires selecting a suitable multimeter
Most modern multimeters can measure AC signals with frequencies as low as 20Hz. But some applications require measuring signals at lower frequencies. To perform such measurements, you need to select a suitable multimeter and configure it appropriately. Please take a look at these examples:
The multimeter uses digital sampling technology and can perform true RMS measurements as low as 3Hz. It uses digital methods to increase the stability time to 2 or 5 seconds during slow filtering. To perform measurements, you should pay attention to:
1. Setting the correct AC filter is crucial. The filter is used to smooth the output of the true RMS converter. When the frequency is below 20Hz, the correct setting is LOW. When setting the LOW filter, ensure the stability of the multimeter by inserting a delay of 2 to 5 seconds. Set the low filter using the following command.
2. If you know the level of the measured signal, you should set a manual range to help speed up the measurement. The longer stabilization time for each low-frequency measurement will significantly slow down the automatic range.
3. Block the ACRMS converter with a DC blocking capacitor to measure the DC signal. This allows the range used by the multimeter to measure AC components. When measuring sources with high output impedance, it is necessary to ensure sufficient time to ensure the stability of the DC isolation capacitor. The stability time is not affected by the frequency of the AC signal, but is affected by any changes in the DC signal.
There are three methods for measuring ACRMS voltage in T; Its synchronous sampling mode can measure signals as low as 1Hz. To configure the multimeter for low-frequency measurement:
1. Select synchronous sampling mode:
2. When you use synchronous sampling mode, for ACV and ACDCV functions, the input signal is DC coupled. During the ACV function, the DC component is mathematically deducted from the reading. This is an important consideration as the combined AC and DC voltage levels may cause overload conditions, even if the AC voltage itself is not overloaded.
3. Choosing an appropriate range can accelerate measurement, as the automatic range characteristic can cause delays when measuring low-frequency signals.
4. To sample waveforms, a multimeter needs to determine the signal period. Use the ACBAND command to determine the pause value. If you have not used the ACBAND command, the multimeter may pause before the waveform repeats.
5. The synchronous sampling mode triggers the synchronous signal with a level. But the noise on the input signal may cause false level triggering and result in incorrect readings. It is important to choose a level that can provide a reliable trigger source. For example, to avoid the peak of a sine wave, as the signal changes slowly while noise can easily cause false triggering.
6. To obtain the reading, ensure that the environment around you is electrically "quiet" and use shielded test wires. Enable level filtering and LFILTERON to reduce sensitivity to noise.
