The Case for Calibration

What is involved in meter calibration?

Calibration simply stated is applying a known standard to a meter, determining the accuracy as found compared to the standard, and then making the necessary adjustments to bring meter into the manufacturer’s stated accuracy and regulatory compliance.

Calibration and Repair

Who should calibrate my meters?

The International Society of Automation certifies technicians and engineers to perform instrument calibration and tuning. Standards, reagents, thermometers, signal generators and all other references are required to be traceable to NIST. Additionally, you should have an engineer or technician who is not only familiar with meters and controls but also water, wastewater treatment or pharmaceutical, or your particular processes. In addition to college and technical training, are they experienced with your particular process and not just lab equipment? If you are in water or wastewater, are they licensed water or wastewater operators who know and understand your process and requirements? The old adage “you get what you pay for” is especially true when it comes to calibration.

Why should I have my meters calibrated?

The simple answer is you’ll save money today in chemical and process control and it usually saves you money in instrument repair and downtime later on. A commonly found 3% error in a billing meter in a 1 MGD booster station could result in 30,000 gallons per day either being over billed or under billed. If you are paying $ 2.85 per 1,000 gallons pumped and selling for $ 3.85 per 1,000 that is a cost of $ 30.00 per day or $ 10,950.00 per year. The calibration cost at $ 600 to $ 1200 per day annually or semi-annually is a small expense compared to the cost of lost of revenue.

How and When should I have my meters calibrated?

Often we are asked the question, “How often should I have my meters calibrated?” At first this may appear to be a simple question, but it requires a lengthy answer.

1.) Are my meters controlling my process?

Quarterly calibrations are often required to be performed on chlorine, turbidity, fluoride, DO, ORP, pH, TSS or TDS if they are controlling your process and/or the meter data is being used for reporting purposes. Qualified operators and laboratory personnel often provide the quarterly calibration of the turbidity and chlorine process meters. Plant staff is competent to provide quarterly standardization of laboratory equipment as well as plant process instruments. However, we have one note of caution. If the electronics or signal generation is variant in the process meter, the plant staff may not be proficient enough to isolate and analyze the signal to determine corrective measures. This is especially true when multiple items are contained in the process loop. Remember, you should calibrate the entire instrument or control loop from beginning to end. Start at sensor and work all the way through the loop to the final display, recorder, SCADA or PLC.

Wastewater Treatment Plant Instruments and Connection Diagram

2.) Are my meters controlling auxiliary equipment?

In many plants automated water samplers that are flow-paced use the meter signal for flow weighted composite sampling. This same flow signal may also be used to provide chemical pump feed rate, blending, pinch valve control or even UV disinfection lighting bank control. Often times, not only are meters and auxiliary equipment involved, but powered loop isolators are also required to separate and drive the signal to the various items being controlled. Each additional isolator or item added into the control loop introduces more room for error and potential signal variance. Multiple item loop control often means a greater need for regular calibration.

Water Treatment Plant Process Diagram and Connections

3.) Are my meters being used to bill my customers or am I being billed by the meter?

Using meters for billing or billing reconciliation is often the case in large distribution and collection systems where a part of the water is purchased from another agency or a separate agency is receiving wastewater from an isolated lift station. This is a case where calibration should be performed on a regular basis. The advent of modern electronic instruments provides a relatively stable signal unlike years ago when metering was largely electro-mechanical. Aqua Technology Group recommends semiannual calibration on modern electronic meters as a relatively cost effective means of assuring accurate billing data is being generated.

4.) What does my regulatory agency require?

Most state agencies expect at least annual calibration on all meters used for monthly operating reports. This includes our service areas in Ohio, Kentucky, Indiana, Michigan, West Virginia, Virginia, Georgia, Tennessee and throughout the US. Often when plant inspections are performed by the agency, they look for calibration stickers on the meter with calibration date and date next calibration is due. Some agencies require an active certificate of calibration to be on file in the plant office. If you are not sure what your agency requires, ask before your next plant inspection or sanitary survey is conducted. Be proactive and ready to answer the question,”When were your meters last calibrated?”

A quality instrument technician or field engineer will evaluate every aspect of your metering system or process – from start to finish. They will check the sensor, recorders, totalizers, chart pen movement, signal isolators, PLC’s, chemical feed controls, and primary flow devices such as weirs and flumes for proper installation, configuration, level and sizing.

The case for calibration is simple: It saves you money today, tomorrow and down the road on repair and replacement cost. Questions? Contact Aqua Technology Group or call 800-513-8993 to get started with calibration.