Calculated pH Based on Conductivity

Conductivity sensors can do more than just measure conductivity. Calculated values from the M800 Transmitter using conductivity data can provide valuable cycle chemistry information, confirm on-line sensor values, save time, and reduce costs.

The low cost and high value of calculated measurements

Calculated pH and other derived measurements from analytical transmitters, are a smart method of providing valuable cycle chemistry information without the cost of additional sensors. And with the decrease in personnel overseeing power plant cycle chemistry today, there is growing reliance on on-line instrumentation.

As conductivity sensors require far less maintenance than pH sensors, calculating pH from conductivity measurements is an excellent way of reducing the burden on maintenance engineers.

Less maintenance is not the only advantage of calculated values. Availability of calculated pH plus on-line pH sensor measurements in the M800 Transmitter provides the best of both worlds: high accuracy by calculation within normal operating conditions, and direct measurement by pH sensors when operation goes out of the normal range. And because specific and cation conductivity measurements are already required for most water samples, the calculated pH value can be obtained at no additional cost.

Early warning of sensor issues


The M800 Transmitter can also display and alarm on the difference between the calculated and the measured pH values. This kind of diagnostic can identify the need for pH sensor maintenance or calibration, or warn of conditions outside the range for accurate pH calculation as well as conditions exceeding cycle chemistry guidelines.

CO2 concentration without a CO2 sensor

A further capability of the M800 is inferring CO2 concentration from cation conductivity and degassed cation conductivity. Degassing the sample is the best means of monitoring condensate to determine how much of the cation conductivity value is due to non-volatile mineral contamination and how much is due to CO2. The M800 transmitter can use those values, along with known CO2 conductivity data, to derive the CO2 concentration on-line. And with the CO2 removed, the remaining degassed cation conductivity can be interpreted as total non-volatile anions with readout on the M800 as ppb chlorides or sulfates.

This white paper discusses how power plants can derive a calculated pH value and a calculated CO2 value from measurements of specific, cation and degassed cation conductivity. These important calculated values can be transmitted via a multi-parameter transmitter for managing and validating a power plant’s water cycle chemistry measurements.
The white paper covers both the underlying scientific principles that allow for the generation of a calculated pH value and a calculated CO2 value, based on the three measured conductivity values, and then explains how this is achieved quickly and directly in a multi-parameter transmitter.

Download the White Paper


Powerful multi-parameter instrument

Cycle chemistry parameters may include specific conductivity, cation conductivity, degassed cation conductivity, calculated pH, pH by sensor, ORP, carbon dioxide, ammonia, dissolved oxygen and flow – all of which can be measured with the M800. The M800 accepts inputs from any combination of four analytical sensors and can derive multiple measurements from each one.

The practice of calculating pH and CO2 from conductivity measurements has been available for a number of years, but typically required complicated hardware and modifications to the PLC / DCS to be able to integrate them. The advanced capabilities of the M800 Transmitter provide unequalled simplicity, flexibility, and convenience for detailed cycle chemistry monitoring.

Visit METTLER TOLEDO Process and Analytics website: https://www.mt.com/pro

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