Online instruments and field meters tell operators what the plant is doing. They drive chemical dosing, trigger alarms and provide the records that show compliance.
An instrument is only useful if its range fits the process, its output fits the control system, and someone can keep it calibrated. Those three questions should shape every purchase.
What falls under this category
- Water quality analysers
- pH and ORP, conductivity and resistivity, turbidity, dissolved oxygen, free and total chlorine, silica, hardness and TOC.
- Field and portable meters
- Handheld instruments for spot checks and sampling rounds.
- Flow measurement
- Electromagnetic, ultrasonic, turbine and variable-area flowmeters.
- Level and pressure
- Ultrasonic, radar and hydrostatic level sensors, and pressure transmitters.
- Data and telemetry
- Data loggers, controllers, SCADA integration and remote monitoring.
Specifications to compare
- Range and resolution
- Suited to the point being measured. Conductivity sensors, for example, use different cell constants for low-conductivity permeate and high-conductivity feed or brine.
- Sensor technology
- Optical dissolved-oxygen sensors generally need less maintenance than galvanic or polarographic ones; chlorine can be measured amperometrically or colorimetrically. Each has different upkeep.
- Flowmeter suitability
- Electromagnetic flowmeters only work on liquids above a minimum conductivity, which can rule them out on high-purity permeate lines. Most flowmeters also need straight pipe runs upstream and downstream.
- Outputs and communication
- 4–20 mA, relays, Modbus, Profibus, Profinet or HART, matched to your PLC or SCADA.
- Enclosure rating
- Ingress protection (for example IP65 or IP68) and hazardous-area certification where needed.
- Calibration and consumables
- Calibration frequency, buffers and standards, reagent consumption and sensor replacement intervals. Reagent-based analysers can cost more to run than to buy.
Information to send suppliers with your enquiry
- Parameter, expected range and required accuracy.
- Process conditions: temperature, pressure, pipe size and material.
- Installation type: inline, insertion, submersion or sample flow cell.
- Control system and signal type.
- Power supply and environment.
- Whether you need traceable calibration certificates.
Common sourcing mistakes
- Choosing the wrong range or conductivity cell for the measuring point.
- Ignoring reagent and sensor running costs.
- Installing flowmeters without the required straight runs, then distrusting the readings.
- No access for maintenance and calibration.
- Using handheld TDS pens for design decisions that need laboratory analysis.