Appx.
7
Causes of Error in Voltage Measurement
Example: Using a measuring instrument with a bias current of 30 pA when dividing a 100 mV
voltage with a
R
1
=
R
2
= 1 M
Ω
resistor yields the following measured value.
mV
985
.
49
pA
30
k
500
M
1
M
1
M
1
mV
100
k
500
M
1
M
1
M
1
M
1
M
1
//
M
1
OUT
=
×
Ω
−
Ω
+
Ω
Ω
×
Ω
=
Ω
+
Ω
Ω
⋅
Ω
=
Ω
Ω
=
R
R
OUT
=
R
1
//
R
2
I
B
V
B
OUT
I
R
V
−
R
1
R
2
Output resistance
Voltage
Bias current
Figure. Effects of Bias Current
Effects of high-voltage measurement
When a high voltage is measured, the instrument’s internal resistance
R
IN
consumes power,
generating heat.
Power consumption
IN
2
R
V
W
=
The input resistance voltage division ratio varies with the amount of heat generated, and
this variation affects measurement. The effect of heat on measured values is included in the
instrument’s specifications as the voltage coefficient error. Generally speaking, caution should be
exercised when measuring voltages in excess of 300 V.
R
IN
V
Input resistance
Voltage
Figure. Effects of High-Voltage Measurement
Effects of burst noise
Burst noise, which is generated by amplifiers used in signal conditioning (shown in A in "Appx. 1
Block Diagram" [p. Appx.1]), consists of microvolt-order voltage shifts that last from several seconds
to several minutes. This type of noise is believed to be caused by lattice defects and contamination
in the amplifier. Although Hioki strives to carry out inspections to reduce burst noise, it is not
possible to completely eliminate this type of noise.
In applications requiring precise measurement, use statistical techniques to ensure the required
level of precision, for example by acquiring multiple data points over an extended period of time
and then eliminating those measured values that deviate from the distribution.
10
9
8
7
6
5
4
3
2
1
Appx.
索
索
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