Meter Calibration for Water & Wastewater Plants
What is involved in meter calibration of a water plant or wastewater plant?
Calibration of water plant meters and wastewater plant meters is simply:
- Applying a known standard to the meter
- Determining the accuracy as found compared to the standard
- Making the necessary adjustments to bring meter into the manufacturer’s stated accuracy and regulatory compliance
Who should calibrate my water meters and plant instruments?
Many in the industry prescribe to the methods from the ISA – International Society of Automation. The ISA certifies technicians and engineers to perform detailed instrument calibration and tuning. All of the standards, reagents, thermometers, signal generators and references are required to be calibrated to a standard regularly and traceable to NIST.
Lab Trained Technician or Real World, Field Experienced Water and Wastewater Calibration Specialist?
Additionally, you should have a field engineer or experienced technician who is not only familiar with meters and controls but also one experienced in water, wastewater treatment processes. In addition to the theory learned in the classroom and technical training, are they experienced with your particular process and not just in lab equipment? If you are in water or wastewater, how long have they been operating in water plants or wastewater plants? Are they also water or wastewater operators who know and understand your process and requirements? Theory in the class or experience gained from other process does not completely translate to the process of water treatment and wastewater treatment.
Why should I have my water or wastewater meters calibrated?
The simple answer is this. You’ll save money and time today in chemical costs and process control. Water and wastewater instrument calibration also typically saves you money in instrument repair and downtime further down the road.
For example, a commonly found 5% error in a water meter or wastewater meter found in a 1 MGD treatment process could result in 50,000 gallons per day either being over reported or under reported. If you are paying $ 3.95 per 1,000 gallons pumped and selling for $ 4.95 per 1,000 that is a cost of $ 50.00 per day or $ 18,250.00 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 or chemical use.
How and When should I have my water meters or wastewater meters calibrated?
When presenting or visiting conferences, we are asked repeatedly the question, “How often should I have my flow meters and other instruments 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. Monthly calibrations are often required for chlorine leak detection, pH for discharge, gas detectors and other safety based instrumentation. Operators and laboratory staff often complete the quarterly calibration of the turbidity and chlorine process meters with calibration kits and standards. Plant staff can be trained and provided with calibration kits to provide in house quarterly standardization of laboratory equipment. However, we have one note of caution. If the 4-20 mA outputs, electronics or signal generation is off in the process meter or loop, the plant staff may not be able to isolate and analyze the individual problem in the loop to determine corrective measures. This is especially true when multiple items are contained in the process loop.
You should calibrate the entire instrument loop or control loop from beginning to end. Start at sensor and then work down the chain, all the way through the loop to the final point of display. This is often a chart recoder, SCADA or PLC.
2.) Are my meters controlling other things in the loop or 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 light bank control. Not only are meters and auxiliary equipment often involved, but powered loop isolators are sometimes required to separate and drive the signal to the various items being controlled. Each additional signal isolator or item added into the full control loop introduces more room for error and the potential for signal variance and error. Multiple item loop control often means a greater need for regular calibration. The more items in the loop, the greater the chance for deviation in complete system accuracy.
3.) Are my water meters or wastewater 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 – quarterly, every six months or annually. The advent of modern electronic instruments provides a relatively stable signal. This is unlike years ago when metering was largely electro-mechanical. MCE service recommends quarterly calibration for analytical instruments and semiannual calibration on modern electronic flow 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 quarterly, semi-annual or at least annual calibration on all meters used for monthly operating reports. This includes our calibration service areas in Ohio, Kentucky, Indiana, Michigan, West Virginia, Virginia, Georgia, Tennessee and throughout the US. When plant inspections are performed by the agency, they tend to look for up to date calibration stickers on the meter with the calibration date and the date that the next calibration is due. Some inspectors or agencies even 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 in the calibration process and always ready to answer the question,”When were your meters last calibrated?”
A quality water plant instrument technician or wastewater treatment plant field engineer will evaluate every aspect of your metering system or process – from start to finish. They will check each sensor, recorders, totalizer, individual chart pen movement, each signal isolator, each PLC input card, each chemical feed controller, and all primary flow devices such as weirs and flumes. Each primary flow device should be checked for proper installation, configuration, level and sizing.
The case for water plant calibration and wastewater plant calibration is simple: Calibration saves you time and money today, tomorrow and down the road on reporting, repair and replacement cost. Questions? Contact MCE Process or call (844) 638-3757 / 844 METER 57 or (937) 500-5208 to get started with your water treatment plant calibration or waste water treatment plant calibration solution.