Step 2: Press on the front panel. Step 3: Press Aperture and choose the number of power-line cycles (PLCs) to use for the measurement. 1, 10, and 100 PLC provide normal mode (line frequency noise) rejection. Selecting 100 PLC provides the best noise rejection and resolution, but the slowest measurements:
Step 4:Press Range to select a range for the measurement. You can also use the [+], [-], and keys on the front panel to select the range. (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 5:
Auto Zero: Autozero provides the most accurate measurements, but requires additional time to perform the zero measurement. With autozero enabled (On), the DMM internally measures the offset following each measurement. It then subtracts that measurement from the preceding reading. This prevents offset voltages present on the DMM’s input circuitry from affecting measurement accuracy. With autozero disabled (Off), the DMM measures the offset once and subtracts the offset from all subsequent measurements. The DMM takes a new offset measurement each time you change the function, range, or integration time. ( There is no autozero setting for 4-wire measurements.)
Step 6:
Specify the input impedance to the test leads (Input Z). This specifies the measurement terminal input impedance, which is either Auto or 10 MΩ. The Auto mode selects high impedance (HighZ) for the 100 mV, 1 V, and 10 V ranges, and 10 MΩ for the 100 V and 1000 V ranges. In most situations, 10 MΩ is high enough to not load most circuits, but low enough to make readings stable for high-impedance circuits. It also leads to readings with less noise than the HighZ option, which is included for situations where the 10 MΩ load is significant.
DCV Ratio
The DCV Ratio key enables or disables DCV Ratio measurement. Note that the Auto Zero softkey disappears when you enable DCV Ratio measurements. This is because autozero cannot be disabled during DCV Ratio. The ratio is the voltage on the Input terminals divided by the reference voltage. The reference voltage is the difference of two separate measurements. These measurements are the DC voltages from the HI Sense terminal to the LO Input terminal and from the LO Sense terminal to the LO Input terminal. These two measurements must be within the range of ±12 VDC. The reference voltage is always autoranged, and the range used for both will be based on the larger result of these two measurements. Configure DCV Ratio measurements as shown:
AC Voltage This section describes how to configure AC voltage measurements from the front panel. NOTE 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 on the front panel.
Step 3: Press Range to select a range for the measurement.
(Auto (auto-range) 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. You should generally select the highest frequency filter whose frequency is less than that of the signal you measure 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.
NOTE For accurately displayed statistics of AC measurements in Front Panel mode, the default manual trigger delay ( > Delay Man) must be used.