To measure low frequencies, select the appropriate multimeter as follows
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 choose a suitable multimeter and configure it appropriately. Please take a look at the following examples:
The Agilent34410A and 34411A multimeters use digital sampling technology and can perform true effective value measurements as low as 3Hz. It increases the stability time to 2 and 5 seconds when using a slow filter through digital methods. To perform the measurement, you should pay attention to:
1. Setting the correct AC filter is crucial. The filter is used to smooth the output of the true effective value 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.
VOLTage: AC: BANDwidthMIN
2. If you know the level of the measured signal, you should set a manual range to help speed up the measurement. The longer stability time of each low-frequency measurement will significantly slow down the automatic range.
We recommend setting the manual range.
34401A uses a DC blocking capacitor to block the ACRMS converter and measure the DC signal. This allows the range used by the multimeter to measure the AC component. 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.
The Agilent 3458A has three methods for measuring ACRMS voltage; Its synchronous sampling mode can measure signals as low as 1Hz. To configure the multimeter for low-frequency measurement:
Select synchronous sampling mode:
SETACV: SYNC
2. When you use synchronous sampling mode, for ACV and ACDCV functions, the input signal is DC coupled. During the ACV function, use mathematical methods to deduct the DC component 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 the appropriate range can accelerate measurement, as the automatic range characteristics 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 display
5. The synchronous sampling mode triggers a synchronous signal with a voltage level. However, 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 and 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.
