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OM-13 Series

Explanation of the principle of the moisture-in-oil analyzer（basis）

Our moisture meter detets the moisture value by measuring the dielectric constant（capacitance） in the oil.
Dielectric constant measurement
Dielectric（Insulator, Semiconductor）has a molecular structure that stores electricity.

H+H
O+2-O
H+2-H+OH+

H+2-It works like a capacitor. The amount of electricity stored diﬀers depending on the diﬀerence inthe molecular structure of the substance. ※See dielectric constant table.
Our moisture meter measures the dielectric constant of the object to be measured, converts it
into an electrical signal, and converts the change into a moisture value.
In actual work, electrodes are often installed in the middle of pipelines, but for the sake of clarity, the parallel plate type is used in this explanation.
We measure the charge between two plates, the detection electrode and the ground electrode.
We perform the measurement in the following procedure.

Detection electrodeA small constant current ﬂows from the sensing electrodeto the ground electrode.

Ground electrode

When the object to be measured is placed between thedetection electrode and the ground electrode, the current
value between the electrodes changes.
The current value is converted to a capacitance value.

Detection electrode【Placing the object to be measured increases the capacitance value.】

Measurement
objectGround electrode・・・Now let's start with the explanation of the main subject, the moisture-in-oil analyzer.

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1. About the oil or water capacitance value.
Detection
Capacitanceconverter0

Please adjust the capacitance converter
to show 0 when there is nothing between
the detection electrode and the groundelectrode.

Capacitanceconverter2

If the place between the electrodes was
ﬁlled with oil, the converter displays 2.

80

If the place between the electrodes wasﬁlled with water, the converter displays
80.

GroundOil

Water

Capacitanceconverter

The converter is detecting the permittivity.
If even one drop of water (80) is mixed in with oil (2), the value displayed by theconverter will increase.
If you adjust the converter so that it displays 0V when there is only oil and no water, and
1V when 1% of water is mixed, it will display 2V when 2% of water is mixed.
The capacitance value changes linearly according to the moisture value.

Displayded value（V）
Moisture value（%）

The capacitance value changes linearly according
to the moisture value.

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2. Temperature correction.
The measured value of capacitance depends on the temperature of the object to be measured.
We will explain using the case of measuring the moisture content in oil as an example.
In most cases, the measured value of capacitance will decrease as the oil temperature
increases.

After

Capacitance

Capacitance

Before（pF）（pF）

0 Temperature

（℃）

100

0 Temperature

Temperature ofmeasured oil（℃） 100

Temperature ofmeasured oil

3. System conﬁguration.
ElectrodeConverter
Control unit
& display

Temperaturetransducer.

1. The value measured by the capacitance converter is corrected by the controller anddisplay using the value measured by 2. the temperature transducer.

4. Precautions for use.
Avoid air bubbles.
Keep the pressure constant, because air bubbles are generated due topressure changes.
Make sure it is properly calibrated before use.

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