Digital Multimeter HDM3055 Series Manual

WisdomAugust

This table gives an additional error for each waveform, to be added to the value from the accuracy

table provided in the instrument's data sheet.

The specifications are valid for CF ≤ 10, provided there is insignificant signal energy above the 300 kHz

bandwidth for voltage, or the 10 kHz bandwidth for current. Multimeter performance is not specified for

CF > 10, or when significant out-of-band signal content is present.

Example

A pulse train with level 1 Vrms, is measured on the 1 V range. It has pulse heights of 3 V (that is, a Crest Factor of 3) and duration 111 ?s. The prf can be calculated to be 1000 Hz, as follows:

file:///C:/Users/ADMINI~1/AppData/Local/Temp/ksohtml6328/wps3.png

Thus, from the table above, this AC waveform can be measured with 0.18 percent additional error.

WisdomAugust

Other Primary Measurement Functions

Frequency and Period Measurement Errors

           

The multimeter uses a reciprocal counting technique to measure frequency and period. This method

generates constant measurement resolution for any input frequency. The multimeter's AC voltage

measurement section performs input signal conditioning. All frequency counters are susceptible to

errors when measuring low–voltage, low–frequency signals. The effects of both internal noise and

external noise pickup are critical when measuring "slow" signals. The error is inversely proportional

to frequency. Measurement errors also occur if you attempt to measure the frequency (or period)

of an input following a DC offset voltage change. You must allow the multimeter's input DC blocking

capacitor to fully settle before making frequency measurements.

WisdomAugust

DC Current

When you connect the multimeter in series with a test circuit to measure current, a measurement

error is introduced. The error is caused by the multimeter's series burden voltage. A voltage is

developed across the wiring resistance and current shunt resistance of the multimeter, as shown

below.

WisdomAugust

Avoid applying signals to unused current input terminals

If signal inputs are applied to terminals not needed for the current measurement, measurement

errors may occur. The unused terminals are still protected but the un-needed signals may interfere

with current measurement. For example, applying inputs to the 3A terminals while making

measurements on the 10A terminals will typically cause errors.

The Hi and Lo sense terminals are not used for many measurements. Applying signals here when

not needed can also cause errors. AC or DC voltages above 15 volts peak on the un-needed sense

terminals are likely to cause measurement errors. If unexpected errors are occurring, signals on the

un-needed terminals is an area to check.

WisdomAugust

Temperature Measurements

Temperature measurements require a temperature transducer probe. The supported probes are

2-wire and 4-wire RTDs, 2-wire and 4-wire thermistors.

Probe Type Choice

RTD's provide very accurate, highly linear relationships between resistance and temperature,

over a range of roughly –200 to 500 °C. There is very little conversion complexity for an RTD

because it is so intrinsically linear. The multimeter provides measurement for the IEC751 standard

RTD, which has a sensitivity of 0.385%/°C.

WisdomAugust

Thermistor Requirements

The DMM converts the measured thermistor resistance to temperature using the Steinhart-Hart

thermistor equation:

1?T = A + B (Ln(R)) + C (Ln(R))3

Where:

A, B, and C are constants provided by the thermistor manufacturer and derived from three

temperature test points.

R = Thermistor resistance in Ω.

T = Temperature in degrees K.

WisdomAugust

Important: Use only a 5 k? 44007-type thermistor. This type thermistor has constants of A = 1.285e-3,

B = 2.362e-4, C = 9.285e-8. Using an incorrect type of thermistor can result in errors greater than 20 °C

for a temperature being measured of 100 °C.

2-Wire vs. 4-Wire Measurements

As with resistance measurements, 4-wire temperature measurements are more accurate, because errors

due to lead wire resistance are completely eliminated. Alternatively, you can use the multimeter’s Null function

to remove the test lead resistance from the measurement (see NULL Reading below).

WisdomAugust

NULL Reading

The DMM allows a separate null setting to be saved for the temperature function. When making

null measurements, each reading is the difference between a stored null value and the input signal.

One application of NULL is to increase accuracy of two-wire resistance measurements by first nulling

the closed–circuit test lead resistance.

Autozero On/Off

Enabling the autozero feature (ON) provides greater accuracy; however, the additional measurement

(of zero) reduces the reading speed.

WisdomAugust

Making High–Speed AC Measurements

The multimeter's AC voltage and AC current functions implement three low–frequency filters.

These filters allow you to trade–off minimum measured frequency for faster reading speed.

The FAST filter settles in 0.025 seconds, and is useful for frequencies above 200 Hz. The

MEDIUM filter settles in 0.625 seconds for voltage and 0.25 seconds for current, and is useful

for measurements above 20 Hz. The SLOW filter settles in 2.5 seconds for voltage and 1.66

seconds for current, and is useful for frequencies above 3 Hz.

WisdomAugust

With a few precautions, you can perform AC measurements at speeds up to 500 readings per second.

Use manual ranging to eliminate auto-ranging delays. By setting the trigger delay to 0, the FAST, MEDIUM,

and SLOW filters allow up to 500, 150, and 50 readings per second, but with reduced accuracy because

the filter may not fully settle. If the sample–to–sample levels are similar, little settling time is required for

each new reading. Under this specialized condition, the MEDIUM filter provides reduced accuracy results

at 20 readings per second, and the FAST filter provides reduced accuracy results at 200 readings per second.