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Author: WisdomAugust

Digital Multimeter HDM3055 Series Manual

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 Author| Post time 2024-6-13 08:05:23 | Show all posts
Measurements Below Full Scale

You can make the most accurate AC measurements when the multimeter is at or near the full scale
of the selected range. Autoranging occurs at 10% (down–range) and 120% (up–range) of full scale.
This enables you to measure some inputs at full scale on one range and 10% of full scale on the
next higher range. In general, the accuracy is better on the lower range; for the highest accuracy,
select the lowest manual range possible for the measurement.


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 Author| Post time 2024-6-14 10:02:46 | Show all posts
High-Voltage Self-Heating Errors

If you apply more than 300 Vrms, self–heating occurs in the multimeter's internal signal–conditioning
components. These errors are included in the multimeter's specifications. Temperature changes inside
the multimeter due to self–heating may cause additional error on other AC voltage ranges. The additional
error is less than 0.02% and dissipates in a few minutes.


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 Author| Post time 2024-6-15 11:28:54 | Show all posts
Edited by WisdomAugust at 2024-6-17 08:16

AC Current Measurement Errors (Burden Voltage)

Burden voltage errors, which apply to DC current, also apply to AC current measurements. However,
the burden voltage for AC current is larger due to the multimeter's series inductance and your
measurement connections. The burden voltage increases as the input frequency increases.
Some circuits may oscillate when performing current measurements due to the multimeter's
series inductance and your measurement connections.



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 Author| Post time 2024-6-17 08:18:41 | Show all posts
Low–Level Measurement Errors

AC voltage measurements less than 100 mV are especially susceptible to errors introduced by
extraneous noise sources. An exposed test lead acts as an antenna and a properly functioning
DMM will measure the signals received. The entire measurement path, including the power line,
act as a loop antenna. Circulating currents in the loop create error voltages across any
impedances in series with the DMM's input. Therefore, you should apply low–level AC
voltages to the DMM through shielded cables, with the shield connected to the input LO terminal.


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 Author| Post time 2024-6-18 08:08:53 | Show all posts
Connect the DMM and the AC source to the same electrical outlet whenever possible.
You should also minimize the area of any ground loops that cannot be avoided. A
high–impedance source is more susceptible to noise pickup than a low–impedance
source. You can reduce the high–frequency impedance of a source by placing a
capacitor in parallel with the DMM's input terminals. You may have to experiment
to determine the correct capacitor for your application.


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 Author| Post time 2024-6-19 09:30:39 | Show all posts
Edited by WisdomAugust at 2024-6-20 08:52

Most extraneous noise is not correlated with the input signal. You can determine the error as shown
below.



Correlated noise, while rare, is especially detrimental because it always adds directly to the input signal.
Measuring a low–level signal with the same frequency as the local power line is a common situation that
is prone to this error.



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 Author| Post time 2024-6-20 08:54:29 | Show all posts
Common Mode Errors

Errors are generated when the multimeter's input LO terminal is driven with an AC voltage relative
to earth. The most common situation where unnecessary common mode voltages are created is
when the output of an AC calibrator is connected to the multimeter "backwards." Ideally, a multimeter
reads the same regardless of how the source is connected. Both source and multimeter effects can
degrade this ideal situation. Because of the capacitance between the input LO terminal and earth
(approximately 200 pF), the source will experience different loading depending on how the input is
applied. The magnitude of the error is dependent upon the source's response to this loading.
The DMM's measurement circuitry, while extensively shielded, responds differently in the backward
input case due to slight differences in stray capacitance to earth. The DMM's errors are greatest for
high– voltage, high–frequency inputs. Typically, the DMM exhibits about 0.06% additional error for a
100 V, 100 kHz reverse input. You can use the grounding techniques described for DC common mode
problems to minimize AC common mode voltages.


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 Author| Post time 2024-6-21 09:33:27 | Show all posts
Leakage Current Errors

The DMM's input capacitance will "charge up" due to input bias currents when the terminals are
open–circuited (if the input resistance is >10 G?). The DMM's measuring circuitry exhibits
approximately 30pA of input bias current for ambient temperatures from 0 to 30 °C. Bias
current doubles for every 8 °C change in ambient temperature above 30 °C. This current
generates small voltage offsets dependent upon the source resistance of the DUT. This effect
becomes evident for a source resistance of greater than 100 k?, or
when the DMM's operating temperature is significantly greater than 30 °C.



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 Author| Post time 2024-6-24 08:13:17 | Show all posts
Unnecessary Signal Errors

Both 3A and 10A terminals are available for AC and DC current measurements. If signals are applied
to terminals not being used for the current measurement, measurement errors may occur. The
unused terminals are protected but the additional signals may interfere with current measurements.
For example, applying inputs to the 3A terminals while making measurements on the 10A terminals
will typically cause errors.

Unnecessary signals applied to the Hi and Lo Sense terminals can also cause errors. AC or DC
voltages above 15 volts peak on the sense terminals are likely to cause measurement errors.


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 Author| Post time 2024-6-25 09:12:49 | Show all posts
How Sample Rate/Interval is Determined

The DMM always attempts to make the sample interval greater than the expected time required
to take the measurements. A number of settings go into the calculation of the minimum allowable
sample interval. These settings include the measurement function, NPLC, aperture, autorange,
autozero, offset compensation, AC filter, TC open check and gate time.

For example, when autorange is on, the assumption is that no more than one range change will
be required. If more than one level of change occurs, the measurement may be delayed and an
error will be issued.


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