Digital Multimeter HDM3055 Series Manual

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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

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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:

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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.

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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.)

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Step 4:Press Range to select a range for the measurement. You can also use the [+], [-], and

[Range] 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.

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Step 2: Press [DCV] 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:

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Measurements

DC Voltage

This section describes how to configure DC voltage measurements from the front panel, including

DCV ratio measurements.

Step 1: Configure the test leads as shown.

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