Emerson PN 51-1055pHC/rev.K instruction manual Calibrating AN IN-SERVICE Sensor Conductivity

FIGURE 6-2. Calibration Against a Standard Cell

To ensure adequate flow past the sensor during calibration, take the sample downstream from the sensor. For best results, use a flow-through standard cell. If the process tem- perature is much different from ambient, keep connecting lines short and insulate the flow cell.

MODEL SOLU COMP II	SECTION 6.0
	CALIBRATION

6.8 CALIBRATING AN IN-SERVICE SENSOR — CONDUCTIVITY

6.8.1 Purpose

1.After a conductivity sensor has been in service for a period of time, recalibration may be necessary.

2.There are three ways to calibrate a sensor.

a.Use a standard instrument and sensor to measure the conductivity of the process stream. It is not necessary to remove the sensor from the process piping. See Figure 6-2. The temper- ature correction used by the standard instru- ment may not exactly match the temperature correction used by the Solu Comp II. To avoid

errors, turn off temperature correction in the both the analyzer and the standard instru- ment.

b. Place the sensor in a solution of known conduc- tivity and make the analyzer reading match the conductivity of the standard solution. Use this

method if the sensor can be easily removed from the process piping and a standard is available. Be care- ful using standard solutions having conductivity less than 100 µS/cm. Low conductivity standards are high- ly susceptible to atmospheric contamination. Avoid calibrating sensors with 0.01/cm cell constants against conductivity standards in the range 100 to 300 µS/cm. The resistance of these solutions may be too low for an accurate measurement. Calibrate sensors with 0.01/cm cell constant using method c. For addition- al information, see ASTM D5391.

c.To calibrate a 0.01/cm sensor, check it against a standard instrument and 0.01/cm sensor while both sen- sors are measuring water having a conductivity between 5 and 10 µS/cm. To avoid drift caused by absorp- tion of atmospheric carbon dioxide, saturate the sample with air before making the measurements.

6.8.2Procedure-Calibration against a standard meter and cell

1.Calibration against a standard meter and cell transfers the calibration of the standard instrument to the process instrument.

2.Calibrate the standard meter and cell using an accepted procedure, for example ASTM D 1125, Standard Methods 2510, or equivalent. A portable, calibrated standard meter and cell is available from Rosemount Analytical (Model Number 1055C-01-99SQ SQ6053).

3.Most conductivity instruments automatically correct measured conductivity to the value at 25°C. Different instruments may apply slightly different temperature corrections. To avoid errors during calibration, turn off automatic temperature correction in both the analyzer and the standard meter.

NOTE

If a portable reference meter is not available and the conductivity of the grab sample must be determined in the laboratory, temperature correction in both the Solu Comp II and the laboratory instrument MUST REMAIN ON. Be sure that the reference instrument and the Solu Comp II are applying the same temperature correction.

4. Turn off temperature correction.

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