This section describes how to configure AC voltage measurements from the front panel.
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Default delays are selected to give correct first readings for most measurements. For the most accurate measurements, the input blocking RC time constant must settle to 1/50 of the AC signal level. Signals greater than 300 V (rms) or 1 A (rms) will cause self-heating in signal-conditioning components. These errors are included in the instrument specifications. Internal temperature changes due to self-heating may cause additional error on other functions or ranges. The additional error will generally dissipate within a few minutes. For example, consider a 100 mVAC signal with a 10 VDC bias. The 10 VDC bias should be settled to 1/50 of 100 mVAC, or 2 mVDC. The corresponding settling time can be calculated using the blocking RC time constant of 0.22 s as follows: settling time = ln(bias/settled value) * 0.22 s settling time = ln(10 VDC / 2 mVDC) * 0.22 s settling time = ln(5000) * 0.22 s = 1.9 s This additional settling delay should be applied after connecting the signal to the DMM's ACV input or after selecting the ACV function with the signal already connected. If the DC bias remains constant, subsequent measurements can be made to full accuracy without additional settling delays. |
Step 1: Configure the test leads as shown.
Step 2: Press [ACV] on the front panel.
Step 3: Press Range to select a range for the measurement. (Auto (autorange) automatically selects the range for the measurement based on the input. Autoranging is convenient, but it results in slower measurements than using a manual range. Autoranging goes up a range at 120% of the present range, and down a range below 10% of the present range.
Step 4: Press AC Filter and choose the filter for the measurement. The instrument uses three different AC filters that enable you either to optimize low frequency accuracy or to achieve faster AC settling times following a change in input signal amplitude.
The three filters are 3 Hz, 20 Hz, and 200 Hz, and you should generally select the highest frequency filter whose frequency is less than that of the signal you are measuring, because higher frequency filters result in faster measurements. For example, when measuring a signal between 20 and 200 Hz, use the 20 Hz filter.
If measurement speed is not an issue, choosing a lower frequency filter may result in quieter measurements, depending on the signal that you are measuring.
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For accurate displayed statistics of AC measurements in Front Panel mode, the default manual trigger delay ([Acquire] > Delay Man) must be used. |