DL/T 677-2018 in English

ChinaStandards.net is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.

This standard is drafted in accordance with the rules given in GB/T 1.1-2009 Directives for standardization—Part 1: Structure and drafting of standards.

Attention is drawn to the possibility that some of the elements of this standard may be the subject of patent rights. The issuing authority of this standard shall not be held responsible for identifying any or all such patent rights.

This standard is a revision of DL/T 677-2009, including the main technical contents:

——The definition of on-line checking is added.

——The technical requirements of various on-line chemical instruments are modified.

——The complete machine error test principle, complete machine error calculation equations and technical requirements of various on-line chemical instruments are modified.

——Some test items of on-line chemical instruments are deleted.

——Relevant annexes and tables are modified according to the revised contents.

This standard was proposed by the China Electricity Council (CEC).

This standard is under the jurisdiction of Technical Committee on Power Plant Chemistry of Standardization Administration of Power Industry (DL/TC13).

The previous editions of standards replaced by this standard are as follows:

——DL/T 677-1999 and DL/T 677-2009.

In the process of implementing this standard, the relevant comments and recommendations, whenever necessary, may be fed back to the Standardization Center of China Electricity Council (No.1, 2nd Lane, Baiguang Road, Beijing, 100761, China).

Inspection code of on-line chemical instruments for power plant

1 Scope

This standard specifies the technical requirements, test conditions and test methods of on-line instruments for conductivity, pH, sodium ion, dissolved oxygen and silicate in power plants.

This standard is applicable to the acceptance test of the above-mentioned on-line chemical instruments in power plants when they are newly purchased and the measurement test during operation. It may also serve as a reference for laboratory chemical instruments.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

GB/T 6903 Analysis of water used in boil and cooling system—General rule
GB/T 12148 Methods for analysis of water for boiler and for cooling—Determination of total silicon—Photometric method by conversion with hydrofluoric acid for low silicon
GB/T 12149 Analysis of water used in boiler and cooling system—Determination of silica—Molybdenum blue colorimetry
GB/T 13966 Terminology for analytical instruments
GB/T 27501 Preparation method of buffer solutions for the measurement of pH value
DL/T 913 Quality inspection guide for water quality analyzers in thermal power plant
JJG 119 Verification regulation of laboratory pH meters
JJG 291 Dissolved oxygen meter with covered-membrane-electrode
JJG 376 Electrolytic conductivity meters
JJG 757 Verification regulation of ionometers

 
3 Terms and definitions

For the purpose of this standard, the following terms and definitions apply.

3.1
on-line chemical instruments
on-line industrial process composition analysis instrument specially used for chemical supervision in the production process of power plants, that is, on-line industrial chemical analysis instrument. In the electric power industry, in order to distinguish electrical measuring instruments from thermal instruments, it is called on-line chemical analysis instruments, referred to as on-line chemical instruments for short

3.2
on-line checking
method for local on-line inspection of on-line chemical instruments, or simulating the normal measurement state of on-line chemical instruments to continuously introduce standard water samples close to the measured water samples into the on-line chemical instruments for accuracy inspection

3.3
operating error
error measured at any point within normal operating conditions

3.4
indication error
difference between the indication value of the instrument and the measured [agreed] true value

3.5
fiducial error
ratio of instrument's indication error to fiducial value

Note: The fiducial value of this standard adopts the maximum value in measuring range.

3.6
maximum value in measuring range—M
minimum value one order of magnitude higher than the standard value of the water sample monitored by the instrument

Note: See Annex A for M values of different water samples.

 
3.7
display devices fiducial error
ratio of the indication error of the display device to the maximum value in measuring range of the display device

3.8
temperature compensation additional error
error generated when the instrument is used under non-standard conditions, called additional error. In order to test the self compensation performance of the instrument under different temperature conditions, this index is defined as the temperature compensation additional error

3.9
sample line leakage additional error
relative error of instrument indication value caused by leakage of measurement system

3.10
zero error
error of indication measured by the instrument when the agreed true value is zero

3.11
stability
ability of a measuring instrument to keep its measuring characteristics constant under specified conditions and to keep it constant during continuous operation within a certain period of time (24h)

3.12
repeatability
degree of consistency of a series of results measured by using the same method, the same specimen and under the same conditions. The same conditions include the same operator, the same instrument, the same laboratory and a short time interval

Note: Repeatability represents the random error of instrument, excluding drift and backlash.

3.13
indication of a measuring instrument
value measured and displayed by the measuring instrument

3.14
standard material
material with sufficient accuracy to calibrate or verify instruments, evaluate measurement methods or assign values to other materials

4 Quality acceptance of on-line chemical instruments

4.1 On-line chemical instruments shall be accepted according to the requirements of this standard. See Tables 1, 2, 4, 5, 7, 8, 10, 11 and 13 for specific testing items and technical requirements.

4.2 The standard instruments and devices (standard conductivity meter, standard hydrogen exchange column, standard pH meter, and mobile pH, sodium, dissolved oxygen standard water sample preparation device) used to inspect the on-line chemical instruments of the pure water system shall be traceable and qualified by the primary laboratory of chemical instruments in the power plant.

5 On-line conductivity meter

5.1 Technical requirements

5.1.1 The test items, technical requirements and test cycles of complete machine of on-line conductivity meter shall meet those specified in Table 1.

Table 1 Test items, technical requirements and test cycle of complete machine of on-line conductivity meter
Item Requirements Test cycle
In operating After overhaul Newly purchased
Test for complete machine a Operating error δG
% −10<δG<10 Once per month b √ √
Fiducial error δZ
% −1<δZ<1 Once per month b √ √
a Test the operating error or fiducial error according to the test principle for complete machine specified in 5.4.1.
b For on-line conductivity meters that have passed the test for three consecutive test cycles, the test cycle may be relaxed to once every three months.

5.1.2 When the test result of complete machine is unqualified, the items given in Table 2 shall apply.

Table 2 Test items, technical requirements and test cycles of display device and others of on-line conductivity meter
Item Requirements Test cycle
In operating After overhaul Newly purchased
Test for display device Fiducial error δY
% −0.3<δY<0.3 As required a — √
Temperature compensation additional error δt
×10-3 °C-1 −0.3<%t<0.3 As required a — √
Electrode constant error δD
% −1<δD<1 As required a — √
Exchange column additional error δJ
% −3<δJ<3 As required a — √
Temperature measurement error t
°C –0.5<t<0.5 As required a — √
a When the test result of complete machine is unqualified, the items in this table shall apply.

5.2 Test conditions

The test conditions for on-line conductivity meter shall meet those specified in Table 3.

Table 3 Test conditions for on-line conductivity meter
Test condition Specifications and requirements
Temperature of water sample
°C 5–50
Flow of water sample Flow required by instrument manufacturer

5.3 Test equipment and standard solution

5.3.1 The standard conductivity meter shall meet the following requirements at the same time:

a) the complete machine fiducial error shall not be greater than ± 0.5%.

b) capable of measuring flowing water samples.

c) at least has the function of non-linear temperature compensation for mixed bed effluent water sample, ammonia-containing water sample, hydrogen type cation exchange column effluent or other cation exchange equipment effluent water samples.

d) capable of eliminating the influence of differential capacitance on electrode surface and distributed capacitance of wire.

e) regularly verified to meet the value transfer conditions.

5.3.2 Standard AC resistance box and DC resistance box with accuracy better than Grade 0.1.

5.3.3 Precision thermometer, with measuring range of 0°C–50°C and minimum division value of 0.1°C.

5.3.4 Adjustable constant temperature water bath with accuracy of ± 2°C and range from ambient temperature to 50°C.

5.3.5 The standard hydrogen exchange column shall meet the following requirements at the same time:

a) equipped with hydrogen cation exchange resin with regeneration degree greater than 98%.

b) the resin crack is less than 1%.

c) the exchange column additional error not exceed ± 2%.

Note: Other types of cation exchange equipment meeting the above conditions may be used for standard hydrogen exchange columns.

5.3.6 Potassium chloride standard solution

Note: The conductivity standard solution may be prepared according to B.1 and B.2 in Annex B.

5.3.7 Device capable of continuously producing stable low conductivity water samples.

5.4 Test for the complete machine error

5.4.1 Test principles

For the conductivity meter measuring the conductivity value of water sample not greater than 0.30 μS/cm, the on-line checking shall be adopted to test the complete machine operating error; for conductivity meter measuring the conductivity value greater than 0.30 μS/cm, the on-line checking should be adopted to test the complete machine operating error, or the off-line test method of static standard solution may be adopted to test the complete machine fiducial error.

5.4.2 Test for complete machine operating error (on-line checking)

For the instrument measuring direct conductivity, connect the conductivity cell of the standard meter in parallel (or in series) with the conductivity cell of the tested meter nearby according to Figure 1, and the water sample of the tested meter during normal measurement is used; for the instrument measuring hydrogen conductivity, connect the conductivity cell of the standard meter and the conductivity cell of the tested meter to the standard hydrogen exchange column and the on-line hydrogen exchange column respectively as shown in Figure 2, and the water sample of the tested meter during normal measurement is used. The flow rate of water sample shall be adjusted according to the requirements to meet the conditions specified in Table 2 and remain relatively stable. After the measured values of the tested meter and the standard meter are stable, accurately read the conductivity indication of the tested meter (κJ) and conductivity indication of standard meter (κbB) and record the temperature indication of the standard meter. See Table C.1 in Annex C for the record format of test data.


Figure 1 Schematic diagram of test for complete machine operating error of conductivity meter


Figure 2 Schematic diagram of test for complete machine operating error of hydrogen conductivity meter

See Equation (1) for the calculation method of the complete machine operating error.

(1)

where,

δG——the complete machine operating error, %;

κJ——the conductivity indication of tested meter, μS/cm;

κbB——the conductivity indication of standard meter, μS/cm.

Note: If the conductivity of the water sample is unstable, the device capable of continuously producing stable low conductivity water samples shall be adopted to produce stable conductivity water samples, and the conductivity of the water samples shall be less than 0.30 μS/cm.

5.4.3 Test for complete machine fiducial error (off-line test method of static standard solution)

First, set the electrode constant of the tested meter to be consistent with the electrode constant of the supporting electrode of the instrument, and select the standard solution with conductivity greater than 100 μS/cm and in the measuring range of the tested meter. Thermostate the standard solution to 25°C ± 2°C, put the conductivity electrode of the tested meter into the standard solution, and record the conductivity value (κb) of the standard solution after the temperature is stable, accurately read the indication value (κJ) of the tested meter and the temperature value of the solution. See Table C.2 in Annex C for the record format of test data.

See Equation (2) for the calculation method of the complete machine fiducial error.

(2)

where,

δZ——the complete machine fiducial error, %;

κJ——the conductivity indication of tested meter, μS/cm;

κb——the conductivity of standard solution, μS/cm. The conductivity value of standard solution at reference temperature (25°C) can be found from Table B.1 in Annex B according to the prepared potassium chloride standard solution;

M——the maximum value in measuring range, μS/cm.

Note: If the electrode constant is equal to or less than 0.1 cm-1, the complete machine operating error shall be tested according to 5.4.2.

5.5 Test for display device

5.5.1 Test for fiducial error

5.5.1.1 Test principle

For the conductivity meter with measured conductivity value greater than 0.30 μS/cm, the standard AC resistance box (see Figure 3) shall be used as the standard input signal of conductivity for testing. For conductivity meters with measured conductivity value not greater than 0.3 μS/cm, analog circuits (see Figure 4) shall be used as standard signals of conductivity for testing.

5.5.1.2 Test method

Standard AC resistance box and standard DC resistance box with accuracy better than Grade 0.1 are used to simulate solution equivalent resistance RX and temperature resistance Rt respectively as the analog signal of test. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 25°C. Set the conductivity cell constant of the tested meter to 0.01 (or 0.1). The connection between the tested meter and the standard AC resistance is shown in Figure 3. For the conductivity meter with measured conductivity value not greater than 0.30 μS/cm, the AC resistance box RX in Figure 3 is replaced by the analog circuit in Figure 4, where, RX is a standard AC resistance box.


Figure 3 Connection between the tested meter and the standard resistance box


Figure 4 Analog circuit for test of display device of pure water conductivity meter

After the measured value of the tested meter is stable, the analog equivalent resistance signal is input to the display device according to the calculation result of Equation (3).

(3)

where,

RX——the equivalent resistance, Ω;

J——the conductivity cell constant set by the tested meter, cm-1;

κL——the theoretical conductivity, μS/cm.

Record the electrical conductivity indication value, κS, of the tested meter. See Equation (4) for the calculation method of fiducial error of display device. See Table C.3 in Annex C for the record format of test data.

(4)

where,

δY——the fiducial error of display device, %;

κS——the conductivity indication of tested meter, μS/cm;

κL——the theoretical conductivity, μS/cm;

M——the maximum value in measuring range, μS/cm.

 
5.5.2 Test for temperature compensation additional error of display device

Standard AC resistance box and standard DC resistance box with accuracy better than Grade 0.1 are used to simulate solution equivalent resistance RX and temperature resistance Rt respectively as the analog signal of test, which shall be connected in Figure 3.

Set the instrument temperature compensation correctly according to the manual of the tested meter. For example, the non-linear compensation mode for pure water or ultra-pure water is selected to measure the direct conductivity of water samples in mixed bed effluent (desalted water, etc.); the non-linear compensation mode for acidic water sample is selected to measure the hydrogen conductivity of hydrogen cation exchange column effluent water sample; the non-linear compensation mode for ammonia water sample is selected to measure the direct conductivity of ammonia water sample; and the linear compensation of 2% is selected to measure the conductivity of common water sample. The test for temperature compensation additional error of the display device of the on-line conductivity meter used for different types of water samples shall be carried out according to the following procedure:

a) measure the effluent sample of the mixed bed. Set the electrode constant of the tested meter to 0.01 cm-1. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 25°C, and then adjust the solution equivalent resistance RX to 100,000Ω using Equation (3) so that the conductivity displayed by the instrument is 0.1 μS/cm, and record the indication value κt1 of the instrument. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 35°C, calculate the solution equivalent resistance RX as 69,930Ω using Equation (5), adjust RX value as 69,930Ω, and record the indication value κt2 of the instrument.

b) Measure the effluent sample of the hydrogen cation exchange column. Set the electrode constant of the tested meter to 0.01 cm-1. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 25°C, and then adjust the solution equivalent resistance RX to 100,000Ω using Equation (3) so that the conductivity displayed by the instrument is 0.1 μS/cm, and record the indication value κt1 of the instrument. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 35°C, calculate the solution equivalent resistance RX as 72,464Ω using Equation (5), adjust RX as 72,464Ω, and record the indication value κt2 of the instrument.

c) Measure ammonia water samples. Set the electrode constant of the tested meter to 0.1cm-1. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 25°C, and then adjust the solution equivalent resistance RX to 33,333Ω using Equation (3) so that the conductivity displayed by the instrument is 3 μS/cm, and record the indication value κt1 of the instrument. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 35°C, calculate the solution equivalent resistance RX as 28,490Ω using Equation (5), adjust RX value as 28,490Ω, and record the indication value κt2 of the instrument.

d) Measure common water samples. Set the electrode constant of the tested meter to 1cm-1. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 25°C, and then adjust the solution equivalent resistance RX to 2,000Ω using Equation (3) so that the conductivity displayed by the instrument is 500 μS/cm, and record the indication value κt1 of the instrument. Adjust the analog temperature resistance Rt so that the temperature displayed by the instrument is 35°C, calculate the solution equivalent resistance RX as 1,667Ω using Equation (5), adjust RX value as 1,667Ω, and record the indication value κt2 of the instrument.

(5)

where,

RX——the equivalent resistance value of solution at temperature t, Ω;

J——the electrode constant set by the tested meter, cm-1;

κ——the theoretical conductivity at 25°C, μS/cm;

β——the temperature coefficient of solution.

Note: The temperature coefficients of different water samples are measured in the following ways: for the on-line conductivity meter measuring the effluent sample of the mixed bed, the conductivity value at 25°C is 0.1 μS/cm and β is taken as 0.043 at 35°C; for the on-line hydrogen conductivity meter measuring the effluent sample of hydrogen cation exchange column, the conductivity value at 25°C is 0.1 μS/cm and β is taken as 0.038 at 35°C; for the on-line conductivity meter measuring ammonia water sample, the conductivity value at 25°C is 3 μS/cm and β is taken as 0.017 at 35°C; for the on-line conductivity meter measuring common water samples, the conductivity value at 25°C is 500 μS/cm and β is taken as 0.02 at 35°C.

See Equation (6) for the calculation method of the temperature compensation additional error of the display device. See Table C.4 in Annex C for the record format of test.

(6)

where,

δt——the display devices temperature compensation additional error, ×10-3 °C-1;

κt1——the conductivity indication of the tested meter at 25°C, μS/cm;

κt2——the conductivity indication of the tested meter at 35°C, μS/cm;

M——the maximum value in measuring range, μS/cm.

5.6 Test for electrode constant

5.6.1 Test principles

For electrode constants less than 0.1 cm-1, the standard electrode method shall be used for testing. For electrode constants greater than or equal to 0.1 cm-1, the standard electrode method should be used for testing, and the off-line test method of static standard solution may also be used for testing.

5.6.2 Standard electrode method

Connect the standard conductivity cell (with electrode constant of JB) in parallel or series with the tested conductivity cell nearby as shown in Figure 1, and the conductivity of the water sample is within the range of the conductivity of the water sample normally measured by the tested conductivity cell, and keep the conductivity of the water sample unchanged during the test (if the conductivity of the water sample is unstable, use the device required in 5.3.7 to produce the water sample with stable conductivity). Set the temperature compensation mode of standard conductivity meter and tested conductivity meter as no compensation, and record the measured value κb of standard conductivity meter and the measured value κx of the tested conductivity meter after the measured value of the meter is stable. See Equation (7) for the calculation method of the tested electrode constant. See Table C.5 in Annex C for the record format.

(7)

where,

Jx——the tested electrode constant, cm-1;

κb——the measured value of standard conductivity meter, μS/cm;

κx——the measured value of tested conductivity meter, μS/cm;

JB——the electrode constant of standard electrode, cm-1.

5.6.3 Off-line test method of static standard solution

The standard solution with conductivity greater than 100 μS/cm shall be selected when the equivalent resistance of the solution is 5 × 102 Ω to 1 × 104 Ω.

Place the tested electrode in a standard solution with known standard conductivity value (with constant temperature of 25°C ± 2°C). Set the electrode constant of the tested conductivity meter to 1, and measure the conductivity G of the solution.

See Equation (8) for the calculation method of the electrode constant. See Table C.5 in Annex C for the record format.

(8)

where,

Jx——the tested electrode constant, cm-1;

κb——the conductivity of standard solution, μS/cm;

G——the conductance measured by the tested conductivity meter, μS.

5.6.4 Calculation method of electrode constant error

See Equation (9) for the calculation method. See Table C.5 in Annex C for the record format.

δ_D=(J_X-J_g)/J_g ×100% (9)

where,

δD——the electrode constant error, %;

Jx——the tested electrode constant, cm-1;

Jg——the electrode constant given by the manufacturer (or before this calibration), cm-1.

5.7 Test for exchange column additional error

5.7.1 Test methods

Connect the standard conductivity cell to the effluent of the standard hydrogen exchange column, and measure the effluent conductivity κb of the standard hydrogen exchange column by the standard conductivity meter; then connect the standard conductivity cell to the effluent of the tested on-line hydrogen exchange column, and measure the effluent conductivity κz of the tested on-line hydrogen exchange column by the standard conductivity meter.

5.7.2 Calculation method of exchange column additional error

See Equation (10) for the calculation method. See Table C.6 in Annex C for the record format.

δ_J=(κ_z-κ_b)/κ_b ×100% (10)

where,

δJ——the exchange column additional error, %;

κz——the effluent conductivity of on-line hydrogen exchange column, μS/cm;

κb——the effluent conductivity of standard hydrogen exchange column, μS/cm.

Note 1: For the standard hydrogen exchange column and the on-line hydrogen exchange column, the same water sample shall be measured during the test for exchange column additional error, and remain it stable.

Note 2: The hydrogen exchange column used in the on-line hydrogen conductivity meter may adopt other types of cation exchange equipment.

5.8 Test for temperature measurement error

Put the measuring electrode of tested conductivity meter and the standard thermometer into the same aqueous solution, and read the temperature indication tX of the tested meter and standard thermometer indication tB after the reading of the tested meter is stable. The temperature measurement error shall be calculated using Equation (11). See Table C.7 in Annex C for the record format.

t = tX - tB (11)
where,

t——the temperature measurement error, °C;

tX——the temperature indication of tested meter, °C;

tB——the standard thermometer indication, °C. 
6 On-line pH meter

6.1 Technical requirements

6.1.1 The test items, technical requirements and test cycle of complete machine of on-line pH meter shall meet those specified in Table 4.

Table 4 Test items, technical requirements and test cycle of complete machine of on-line pH meter
Test item Technical requirements Test cycle
In operating After overhaul Newly purchased
Test for complete machine a Operating error δG –0.05 < δG < 0.05 Once per month √ √
Indication error δS –0.05 < δS < 0.05 Once per month √ √
Indication repeatability S S < 0.03 As required b — √
Temperature compensation additional error pHt
°C-1 –0.01 < pHt < 0.01 As required c — √
a Test the operating error or fiducial error according to the test principle for complete machine specified in 6.4.1.
b Test it when the meter reading is unstable.
c Test it when the operating error or indication error of complete machine exceeds the standard.

6.1.2 When the test result of complete machine is unqualified, the items given in Table 5 shall apply.

Table 5 Test items, technical requirements and test cycle of display device and electrode of on-line pH meter
Test item Technical requirements Test cycle
In operating After overhaul Newly purchased
Indication error pH –0.03<pH<0.03 As required a — √
Indication error caused by input impedance pHR –0.01 Temperature measurement error t
°C –0.5<t<0.5 As required a — √
Test for reference electrode Internal resistance of reference electrode
kΩ ≤10 As required a — —
Electrode potential stability Within ± 2 mV/8h As required a — —
Test for glass electrode Internal resistance of glass electrode RN
MΩ 5–20 (low resistance);
100–250 (high resistance) As required a — —
Percentage of theoretical slope (PTS)
% ≥ 90 As required a — —
a Test it when the operating error or indication error of complete machine exceeds the standard.

6.2 Test conditions

The test conditions for on-line pH meter shall meet those specified in Table 6.

Table 6 Test conditions for on-line pH meter
Test condition Specifications and requirements
Temperature of water sample
°C 5–50
Flow of water sample Flow required by instrument manufacturer

6.3 Test equipment and standard solution

6.3.1 Low conductivity pH standard water sample preparation device (see Annex D, D.1).

6.3.2 pH meter tester, with an accuracy not less than Grade 0.01.

6.3.3 High resistance switch, with insulation resistance better than 1 × 1012 Ω.

6.3.4 DC resistance box, with accuracy better than Grade 0.1.

6.3.5 For pH standard buffer solution, national metrological standard materials shall be preferred (see Annex E for the preparation method of pH standard solution).

6.3.6 Adjustable constant temperature water bath with accuracy of ± 2°C and range from ambient temperature to 50°C.

6.3.7 Precision thermometer, with measuring range of 0°C–50°C and minimum division value of 0.1°C.

6.3.8 The standard pH meter shall meet the following requirements at the same time:

a) the indication error of pH measurement is less than 0.02.

b) the on-line measurement of pH value of pure water is not affected by electrostatic charge, liquid connection potential and ground loop.

c) capable of eliminating the additional errors caused by the change of slope in Nernst equation, the change of reference electrode potential and the change of solution ion equilibrium constant caused by the change of temperature.

6.4 Test for complete machine error

6.4.1 Test principles

For the on-line pH meter with conductivity of water sample not greater than 100 μS/cm, the on-line checking shall be used for the on-line test of the complete machine operating error. For the on-line pH meter with conductivity of water sample greater than 100 μS/cm, the off-line test method of static standard solution shall be used for the complete machine indication error.

6.4.2 Test for complete machine operating error (on-line checking)

The test for complete machine operating error (on-line checking) may be divided into method 1 and method 2. Method 1 is used to test and measure the pH meter of feed water, condensate water and steam water samples; while Method 2 is used to test and measure the pH meter of furnace water and internal cold water.

Method 1: Introduce the water samples measured by the on-line meter into the sensor inlet of the standard meter and that of the on-line meter respectively, and adjust the flow of the water samples to those specified in Table 5 according to the requirements and remain it relatively stable. After the instrument indication is stable, record the standard meter indication BZ and the tested meter indication Si.

Method 2: The standard water sample is produced by the flowing standard water sample preparation device, and its conductivity shall be within the range of the conductivity of the monitored water sample during the operation of the tested meter. Connect the standard water sample to the sensor inlet of the standard pH meter, and connect the sensor outlet of it to the sensor of the tested meter. After the instrument indication is stable, record the standard meter indication BZ and the tested meter indication Si.

The complete machine operating error is calculated using Equation (12). See Table F.1 in Annex F for the record format.

δG = Si – BZ (12)

where,

δG——the complete machine operating error;

Si——the tested meter indication;

BZ——the standard meter indication.

 
Matters needing attention when carrying out on-line checking are as follows:

a) The conductivity and pH value of the water sample shall be within the normal operation monitoring range of the tested meter.

b) Adjust the flow of water sample within the flow range required by the instrument manufacturer, and remain the pressure of water sample stable.

6.4.3 Test for complete machine indication error (off-line test method of static standard solution)

Place the electrodes of the tested meter in the standard solution with pH = 6.864 (25°C) and pH = 9.182 (25°C) for two-point setting (the standard solution with pH = 7 (25°C) and pH = 10 (25°C) may also be selected according to the instrument instructions), then wash the electrodes, place the electrodes in the standard solution with pH = 4.003 (25°C), and accurately record the indication (Si) of the tested meter, repeat the measurement for three times. See Equation (13) for the calculation method of complete machine indication error. The test result shall be the maximum of δS. See Table F.2 in Annex F for the record format.

δS = Si – Bh (13)

where,

δS——the complete machine indication error;

Si——the instrument indication of the i-th measurement;

Bh——pH value of standard buffer solution.

6.4.4 Repeatability test for complete machine indication

After two-point setting with standard solution, measure another standard solution and record the complete machine indication (pHi) of the tested meter at the same time, repeat the "measurement" operation for 6 times, and express the repeatability by the standard deviation of single measurement result. See Equation (14) for the calculation method. See Table F.3 in Annex F for the record format.
 
(14)

where,

S——the standard deviation of single measurement result;

pHi——the indication of the i-th measurement;

——the average of 6 measurements.

6.4.5 Test for temperature compensation additional error of complete machine

The water sample measured by the on-line meter is connected to the measuring cell of the standard meter and that of the tested meter in turn. After the instrument indication is stable, record the pH indication and temperature t1 of the standard meter. Accurately record the tested meter indication pHJ; adjust the water sample cooler so that the temperature of the standard water sample changes from 5°C to 10°C. After the instrument indication is stable, the pH indication of the standard meter shall remain unchanged, record the temperature t2 of the standard meter and record the tested meter indication pHI. See Equation (15) for the calculation method. See Table F.4 in Annex F for the record format.

(15)

where,

pHt——the temperature compensation additional error of complete machine, °C-1;

pHJ——the tested meter indication before temperature change;

pHI——the tested meter indication after temperature change;

t1——the temperature of standard meter before temperature change, °C;

t2——the temperature of standard meter after temperature change, °C.
 
6.5 Test for display device

6.5.1 Test for display device indication error

6.5.1.1 Connect the wiring as shown in Figure 5, adjust the resistor box so that the instrument temperature is 25°C, and adjust the potentiometer so that its output is zero. For instruments with equipotential (or positioning) regulators, adjust the equipotential (or positioning) regulators to their equipotential pH (for example, for instruments with equipotential 7, adjust pH of the instrument to 7). For instruments with slope (or sensitivity) compensation, the potentiometer may be used to input the equivalent potential value for measuring the upper pH value to the display device [this value may be calculated using Equation (16)], and adjust the slope (or sensitivity) potentiometer so that the display device shows the upper pH value (for example, for instruments with an equivalent potential of 7, the potentiometer outputs –177.471 mV, and adjust the slope (or sensitivity) potentiometer so that the display device shows 10). The slope of the tested meter with conditions may also be set directly at 100%.


Figure 5 Test wiring of display device

6.5.1.2 Adjust the output of the potentiometer using Equation (16) between the actual value of the input potential and the nominal theoretical pH value, and record the indication pHi value of the display device by increasing and decreasing the input of the tested meter once respectively (for example, for a pH meter with an equipotential pH of 7, the output of the potentiometer is 118.31 mV and –118. 31 mV, respectively, and the nominal theoretical pH of the corresponding display device is 5.00 and 9.00, respectively). See Equation (17) for the calculation method of display device indication error. See Table F.5 in Annex F for the record format.

ES = K(pHD – pHB) (16)

pH = pHi – pHB (17)

where,

ES——the input potential value of display device, mV;

K——the theoretical slope, mV, see Annex E, E.3;

pHB——the nominal theoretical pH value of display device;

pHD——the equipotential pH value of tested meter.

pH——the display device indication error during i-th test;

pHi——the error of indication of i-th measurement.

The pH value with the maximum in absolute value shall be taken as the display device indication error

6.5.2 Test for indication error caused by input impedance of display device

Connect the wiring as shown in Figure 6, turn on the high resistance switch K (short circuit of resistance R), and adjust the resistance box so that the instrument temperature is 25°C. Set the value of the tested meter at two points according to 6.5.1.1. Input the potential value of 354.942 mV (equivalent to 6 pH) to the display device by adjusting the potentiometer, and record the indication pH1 of the display device. Disconnect switch K (turn on resistance R). Then input the potential value of 354.942 mV and record the indication pH2 of the display device. Repeat the operation for three times and take its average. See Equation (18) for the calculation method. See Table F.6 in Annex F for the record format.

Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Quality acceptance of on-line chemical instruments
5 On-line conductivity meter
5.1 Technical requirements
5.2 Test conditions
5.3 Test equipment and standard solution
5.4 Test for the complete machine error
5.5 Test for display device
5.6 Test for electrode constant
5.7 Test for exchange column additional error
5.8 Test for temperature measurement error
6 On-line pH meter
6.1 Technical requirements
6.2 Test conditions
6.3 Test equipment and standard solution
6.4 Test for complete machine error
6.5 Test for display device
6.6 Test for temperature measurement error
6.7 Test for electrode performance
7 On-line sodium meter
7.1 Technical requirements
7.2 Test conditions
7.3 Test equipment and standard solution
7.4 Test for complete machine error
7.5 Test for display device indication error
8 On-line dissolved oxygen meter
8.1 Technical requirements
8.2 Test conditions
8.3 Test equipment and standard solution
8.4 Test for complete machine error
8.5 Test for zero error
8.6 Test for temperature influence additional error
8.7 Test for sample line leakage additional error
9 On-line silicon meter
9.1 Technical requirements
9.2 Test conditions
9.3 Standard solution
9.4 Test for the complete machine error
9.5 Test for repeatability of complete machine
9.6 Anti phosphate interference performance test
Annex A (Normative) Maximum value M in measuring range
Annex B (Normative) Preparation method of conductivity standard solution
Annex C (Informative) Record format of on-line conductivity meter test results
Annex D (Informative) Preparation device for low conductivity standard water sample
Annex E (Normative) Preparation method of pH standard buffer solution
Annex F (Informative) Record format of on-line pH meter test results
Annex G (Normative) Preparation and preservation of sodium standard solution
Annex H (Informative) Record format of on-line sodium meter test results
Annex I (Informative) Preparation device for low concentration dissolved oxygen standard water sample
Annex J (Informative) Record format of on-line dissolved oxygen meter test results
Annex K (Normative) Preparation method of silicon dioxide standard solution
Annex L (Informative) Record format of on-line silicon meter test results