JJG 500-2005Verification Regulation of Electrolytic Hygrometers (English PDF)

4.1 Appearance of the instrument (2)

4.2 Instrument Circuit System (2)

4.3 Pneumatic system (2)

4.4 Instrument background value (2)

4.5 Measurement range (2)

5.1 Verification conditions (2)

5.2 Verification items and verification methods (3)

5.3 Processing of verification results (4)

5.4 Verification cycle (4)

Appendix A Electrolytic Hygrometer Calibration Record Format (5)

Appendix B Format of Electrolytic Hygrometer Calibration Certificate and Verification Result Notice (6)

Electrolytic humidity meter verification procedure

1 Scope

This procedure is applicable to the first verification, subsequent verification and in-use inspection of the electrolysis hygrometer. Electrolytic humidity meter for the measurement performance test in type identification or prototype test, refer to this procedure.

2 Overview

Electrolytic humidity meter is widely used in petrochemical, electronic, electric power, metallurgical and other industrial sectors for gas humidity detection.

Includes intermittent measurements and online measurements.

The instrument uses an electrolytic method to measure the humidity in a gas, and the range generally refers to less than 1000 µL/L. The working principle is.

The gas to be measured flows through a special structure of the electrolytic cell, and the water vapor is absorbed by the P2O5 film on the surface of the electrode and is electrolyzed.

For hydrogen and oxygen, P2O5 is regenerated at the end of the reaction. The reaction process can be expressed as.

P2O5 H2O=2HPO3 (1)

2HPO3=H2(up)

2O2(up) P2O5

Merger (1), (2)

H2O=H2(up)

2O2(up)

In the above reaction, the amount of water to be electrolyzed is proportional to the amount of electricity passing through the electrolytic cell. The measured gas continuously passes through the electrolysis the pool in which the water vapor is completely absorbed by the P2O5 film on the surface of the electrode is electrolyzed. When the absorption and electrolysis process is reached at equilibrium, the electrolysis current is proportional to the humidity of the gas. This is the quantitative basis for the instrument.

If the ambient temperature, pressure and measured gas flow rate are known, according to Faraday's law of electrolysis and gas state equations the relationship between the derived electrolysis current and the moisture content of the gas to be measured is.

QpT0FVr10-4

3p0TV0

It can also be simplified as. I=1.4358×10-1VrQ pT0 p0TV0 (µA) (5) in the formula.

I --- electrolysis current of water, µA;

Vr --- the water vapor content of the gas to be tested, µL/L;

Q --- measured gas flow, mL/min;

p --- atmospheric pressure, Pa;

P0 --- standard atmospheric pressure, 101325Pa;

T --- ambient temperature, K;

T0 --- critical absolute temperature, 273.15, K;

F --- Faraday constant, 96484.56C/mol;