Digital Multimeter HDM3055 Series Manual

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Noise Rejection

Rejecting Power–Line Noise Voltages

A desirable characteristic of integrating analog–to–digital (A/D) converters is their ability to reject

power– line related noise present with DC input signals. This is called normal mode noise rejection,

or NMR. The multimeter achieves NMR by measuring the average DC input by "integrating" it over a

fixed period. If you set the integration time to a whole number of power line cycles (PLCs), these

errors (and their harmonics) will average out to approximately zero.

The multimeter provides three integration selections (1, 10, and 100 PLCs) that achieve NMR. The

multimeter measures the power–line frequency (50 Hz or 60 Hz), and then determines the corresponding

integration time. For a complete listing of NMR, approximate added rms noise, reading rate, and resolution

for each integration setting, see the Performance vs. Integration Time table.

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Loading Errors (DC Voltage)

Measurement loading errors occur when the resistance of the DUT is an appreciable percentage of

the multimeter's input resistance, as shown below.

To reduce the effects of loading errors and to minimize noise pickup, set the multimeter's input

resistance to >10 G? (high-impedance) for the 100 mVDC, 1 VDC, and 10 VDC ranges. The

input resistance is maintained at 10 M? for the 100 VDC and 1000 VDC ranges.

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Measurement Tutorial

Follow the suggestions in the sections below to achieve the greatest accuracy with Hantek HDM3000

Series multimeters.

Measurement Considerations

To achieve the greatest accuracy with the Hantek HDM3000 Series multimeters, you must eliminate

potential measurement errors. This chapter describes common errors and suggests ways to avoid them.

DC Measurement Considerations

Thermal EMF Errors

Thermoelectric voltages are the most common error source in low–level DC voltage measurements.

Thermoelectric voltages are generated by circuit connections using dissimilar metals at different temperatures.

Each metal–to–metal junction forms a thermocouple that generates a voltage proportional to the junction

temperature, as shown in the table below. You should minimize thermocouple voltages and temperature

variations in low–level voltage measurements. The best connections use copper–to–copper crimped

connections, as the DMM’s input terminals are a copper alloy.

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Display Options

Display Options configures the display.

You can enable or disable the display, adjust the brightness (1 to 100%). If you turn off the display,

press any front panel key to turn it on again.

Date / Time

Date / Time sets the instrument's real-time clock, which always uses a 24-hour format (00:00:00 to 23:59:59).

There is no automatic setting of the date and time, such as to adjust for daylight savings time.

Use the front panel arrow keys to set the year, month, day, hour, and minute.

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Disables or enables the click heard when a front panel key or softkey is pressed.

Also enables or disables the audible tone (Beeper On or Off) associated with the following features:

l Limits – a measurement limit is exceeded (if limits are enabled)

l Probe Hold – the measured signal records a stable reading

l Diode – the forward bias voltage is between 0.3 and 0.8 V

l Continuity – a short is measured (less than or equal to 10 Ω)

l Error - an error is generated from the front panel or remote interface

This non-volatile setting appears in several different menus on the front panel. Turning the beeper on

or off in one menu affects all of the other menus and functions. For example, turning the beeper off for

probe hold, also turns the beeper off for limits, diode, continuity, and errors.

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User Settings

User Settings specifies user preferences that control how you interact with the instrument. These

settings are stored in non-volatile memory and can be saved in a preferences (.prf) file.

Sounds

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Utility Menu - System Setup

System Setup configures user preferences and sets the date and time.

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Calibrate

Calibrate accesses the instrument calibration procedure. See Calibration for details.

Firmware Update

Firmware Update updates the instrument firmware to a new version. See Firmware Update

for details.

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Utility Menu - Test/Admin

Test/Admin provides access to self-test, calibration, and firmware update function:

Self-Test

Self-Test verifies proper instrument operation. See Self-Test Procedures for details, and always safely

disconnect inputs to the DMM terminals before running the Self Test.