Emerson pH/ORP Sensor 3900VP-02-10

For maximum accuracy, you can standardize the sensor in-line or with a process grab sample after performing a buffer calibration and conditioning the sensor to the process. Standardization accounts for the sensor junction potential and other interferences. Standardization does not change the sensor's slope, but simply adjusts the transmitter's reading to match that of a known process pH

1. While obtaining a process solution sample, record the pH value that is shown on the transmitter display

Emerson recommends taking the sample close to the sensor

2. Measure and record the pH of the process solution sample with another temperature compensated and calibrated pH instrument

For best results, perform standardization at the process temperature

3. Adjust the transmitter to the standardized value;

Prerequisites: Saturated quinhydrone ORP standard solution is available from Emerson (PN R508-8OZ) (460 ± 10 mV); You can also make ORP standard solution by adding a few crystals of quinhydrone to either a pH 4 or pH 7 buffer; Quinhydrone is only slightly soluble; therefore, only a few crystals are required

⚠ WARNING Corrosive substance The solution used during calibration is an acid; handle it with care Follow the directions of the acid manufacturer Wear the proper protective equipment Do not let the solution come into contact with skin or clothing If contact with skin is made, immediately rinse with clean water

Make a temporary electrical connection between the sensor and the transmitter to dissipate any accumulated electrical charge

Immerse the sensor in the standard solution; Allow one to two minutes for the ORP sensor to stabilize

Adjust the ORP value on the transmitter to the solution value shown in Table 4-1 The resulting potentials, measured with a clean platinum electrode and saturated KCl/AgCL reference electrode, should be within ±20 millivolts of the value shown in Table 4-1

Note solution temperature to ensure accurate interpretation of results; The ORP value of saturated quinhydrone solution is not stable over long periods of time; Therefore, make these standards fresh each time they are used

Sign off on the calibration procedure

Erratic readings or sluggish response may indicate that the sensor is dirty and needs to be cleaned; The following are the recommended cleaning procedures for pH/ORP sensors

To remove oil deposits, clean the electrodes with a mild, non-abrasive detergent

To remove scale deposits, soak the electrodes for one to five minutes in a five percent hydrochloric acid solution;

A two-point buffer calibration is the only way to ensure that a pH sensor is providing accurate measurements. During a two-point calibration, the transmitter calculates new values for slope (mV/pH) and zero offset (mV) based on the mV response of the sensor when it is in the pH standard solutions.

1. Immerse the sensor in the first buffer solution. Allow the sensor to adjust to the buffer temperature (to avoid errors due to temperature differences between the buffer solution and sensor temperature) and wait for readings to stabilize.

2. Once the transmitter has acknowledged the first buffer, rinse the buffer solution off the sensor by pouring a small amount of the second buffer solution over the tip of the sensor.

3. Repeat Step 1 using the second buffer solution.

Once the transmitter has acknowledged both buffer solutions, a sensor slope (mV/pH) is established.;