JJG 695-2003Verification Regulation of Sulfur Hydrogen Gas Detectors (English PDF)

3.1 Indication error

The indication error of the instrument is as shown in Table 1.

Table 1

Hydrogen sulfide gas detector

Measuring range Limit of indication error

Molar fraction X (H2S). <= 100 x 10-6 ± 5 x 10-6

Molar fraction X (H2S). > 100 x 10-6 ± 5%FS

3.2 Repeatability

The relative standard deviation shall be not more than 2%.

3.3 Response time

For diffused-type instrument, it is not more than 60 s; for pumped-type instrument, it is not more than 30 s.

observe whether the instrument has alarm sound and whether the alarm light flashes, check the alarm set point of the instrument.

4.2 Insulation resistance

For instruments which use 220V AC, the phase-to-ground insulation resistance of the power supply is not less than 40 Mohm.

4.3 Dielectric strength

For instruments which use 220V AC, the insulation strength of the phase- connected line to ground of the power supply shall be able to withstand the AC voltage of 1500V, 50Hz, for a test duration of 1 min, without breakdown and arcing.

5.1 Verification conditions

5.1.1 Environmental conditions for verification

5.1.1.1 Ambient temperature. 0 ~ 40 °C (fluctuation <= 5 °C)

5.1.1.2 Relative humidity. <= 85%

5.1.2 Equipment for verification

5.1.2.1 Gas reference material

The hydrogen sulfide standard gas which has a concentration of 20%, 50%, 80% of the full scale and 1.5 times the alarm set point is used, which have an uncertainty of not more than 2% (k = 3).

5.1.2.2 Zero calibration gas

High-purity nitrogen or clean air.

5.1.2.3 Flowmeter

(0 ~ 1) L/min, the accuracy level is not less than level 4.

for 1 min, the current is 5 mA. Then the voltage is smoothly lowered to 0 V. The instrument shall not have breakdown and arcing during the whole test.

5.3.4 Indication error

After preheating and stabilization, the instrument uses the zero gas and a standard gas with a concentration of about 80% of the upper limit of the measurement range. After calibrating the zero point and the indication value of the instrument, within the measurement range, respectively lead in the standard gas which has a concentration of about 20% and 50%, respectively, of the upper limit of measurement range (if the instrument has two measuring ranges, it shall lead in at least one standard gas within the low measuring range). Record the actual reading after leading in the gas. Repeat the above procedures for 3 times.

Use the formula (1) or (2) to calculate the indication error of each verification point.

Where.

- The average of the readings;

As - Standard value;

R - Measuring range.

When the instrument's range is > 100 × 10-6, it is calculated by formula (1), take the deltae of the maximum absolute value as the indication error of the instrument.

When the instrument's range is <= 100 × 10-6, it is calculated by formula (2), take the deltae of the maximum absolute value as the indication error of the instrument.

5.3.5 Repeatability

After the instrument is stabilized by preheating and its zero point calibrated by the zero point standard gas, lead in the standard gas which has a concentration of about 50% of the measuring range. After the reading is stable, record the measured value. Repeat the above measuring procedure for 6 times.

Respectively record the reading Ai. The repeatability is indicated by the relative standard deviation deltac. Use the formula (3) to calculate the repeatability of the instrument.

When the instrument's range is > 100 × 10-6, it is calculated by formula (4), take the deltazi of the maximum absolute value as the zero drift of the instrument.

When the instrument's range is <= 100 × 10-6, it is calculated by formula (5), take the deltazi of the maximum absolute value as the zero drift of the instrument.

Calculate the indication drift according to formula (6) or (7).

When the instrument's range is > 100 × 10-6, it is calculated by formula (6), take the deltasi of the maximum absolute value as the indication drift of the instrument.

When the instrument's range is <= 100 × 10-6, it is calculated by formula (7), take the deltasi of the maximum absolute value as the indication drift of the instrument.

5.3.8 Measurement of alarm error

After the instrument is stabilized by preheating, use the zero point gas and the standard gas which has a concentration of about 80% of the upper limit of the measuring range, to calibrate the zero point and the indication value of the instrument. Then lead in the standard gas which has a concentration about 1.5 times the alarm set point (As). Record the actual alarm concentration (Ai) of the instrument. Remove the standard gas. Lead in the zero point gas to zero the instrument. Repeat the above procedures for 3 times. Use the formula (8) to calculate the alarm set error of the instrument.

Take the deltaAi of the maximum absolute value as the alarm set error of the instrument.

5.4 Processing of verification result

The instruments as verified and qualified according to the requirements of this regulation will be issued a verification certificate. The instrument failing to pass the verification will be issued a verification result notice, on which the unqualified items are indicated.

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