4-3
12707 Resistivity Chamber for Liquid Sample Operation Manual
4.2 Discharge and Charge
4.2 Discharge and Charge
(1)
Discharge
Insulation resistance measurement supposes that the surface or inside of the sample is not
charged. However, in fact, charge generation inevitably occurs by friction during trans-
portation or repeated measurement. When a sample to which voltage has been applied in
the past in particular, current back flow or other phenomena that cause measurement er-
rors occur.
To perform precise measurement, discharging the sample is necessary. The discharge time
varies depending on the material or condition of the sample. Generally, the higher the re-
sistance value or dielectric constant is, the longer it takes time.
For how to discharge the sample, refer to Section 3.5 "Measurement."
(2)
Charge
As shown in Figure 4-2, the absorption current occurs after voltage application. This is
caused by a physical phenomenon such as transient polarization state inside of the sample
or by a time constant due to the capacitance of the sample and the input resistance of the
measuring instrument. To terminate such a phenomenon and perform precise current
measurement, the sample needs to be charged.
The charge time varies depending on the sample. Decide the optimal time by performing
measurement several times.
For how to charge the sample, refer to Section 3.5 "Measurement."
4.3 Effect
of
Noise
Insulation resistance measurement is sensitive to external noise such as inductive noise because
low current is measured. Be sure to use a cable of which core wires are wholly shielded such as
a triaxial cable for measurement. Using a cable of which core wires are exposed such as an al-
ligator clip will cause variation or errors in measurement due to inductive noise.
4.4 Effect
of
Vibration
Fan motor vibration or mechanical shock causes variation in measurement and makes the range
unstable. Be careful not to give vibration to the connection cables in particular.
4.5 Securing
Insulation
The following parts in addition to the electrodes need to be insulated.
z
INPUT connector (Figure 2-1 (2)): Clean the center white insulating material.
z
MEASURE terminal (Figure 2-2 (5)): Clean the white insulating material around.
Use a swab soaked in absolute alcohol for cleaning.
For how to clean the electrodes, refer to Section 3.1 "Cleaning the Electrodes."
