Bridging the Digital Divide

A sensor manufacturer that doesn’t use words like smart sensor, IoT, IIoT, big data, analytics in its marketing is a dinosaur. Whether said manufacturer actually knows what these terms mean is another question. We in the water quality instrumentation business are in a particularly challenging technological environment. We and our customers tend to be risk averse. We’ve witnessed claims of superiority for wired digital standards such as Modbus, Profibus, Fieldbus, HART, BACnet or Ethernet/IP. For wireless protocols there’s ISA 100, Zigbee, wireless HART, Thread and LoRa. Pick the wrong one and you end up on the Betamax side of history.

As the world sorts through more competing standards than starting Democratic presidential candidates our industrial universe still continues to insist on 4-20 mA sensors. The limitation of sending only one parameter (unless repackaged as HART) is still an Achille’s heel for this analog survivor but, until a digital winner is anointed, the world of PLC’s will specify them. In fact, we’ve seen more and more orders for 4-20 mA direct output sensors.

AquaMetrix is has been making controllers and transmitters for four decades. The AS-2250 series is our third-generation line and consists of four different models. But, at the same time, we’ve been expanding our direct-output probe sales. For about two decades AquaMetrix has made a 4-20 mA output version of our flagship differential probe. It’s 100% analog circuitry means that it can only be calibrated at the PLC (or AM2300) end, and its output is not electrically isolated. On rare ocassions the latter can be the cause of much anguish. There is a fix: simply put an isolator in line. But a smart probe that encapsulates the essential digital circuitry of a transmitter into the probe body addresses both these shortcomings and others:

1. It leverages the tried-and-true designs of controllers that we spent years perfecting.
2. It employs an RS-485 digital interface to setup, calibrate and diagnose the probe.
3. We can add Modbus onto the RS-485 serial connection and turn the analog output probe into a digital one.
4. The signal is electrically isolated.
5. Adding other digital protocols is straightforward.

We’ve received many requests over the years for a contacting conductivity probe with a so-called blind transmitter. To our surprise we found very few examples amongst our fellow manufacturers. That made it easy to select the first probe to be adapted to this new strategy. The AS-TX conductivity sensor is now out. It combines the front end of our general-purpose AS contacting conductivity probe with a back end containing the circuitry of the AM-2250. It has wires—two for the 4-20 mA loop and two for the RS-485 interface. We can load the firmware via the digital interface and the user can calibrate the probe using that connection to a PC.

The AS-TX looks like it will hold the company record for fastest growing new product. Next up will be our differential pH/ORP probes and our new toroidal probe. The latter, when mated to the AM-2251 controller, can measure a whopping range of 4 to 400,000 µS/cm.

There will always be a case for dumb probes and smart controllers. The controller offers local setup, calibration, relays, PID control, a display and less expensive probes. When a controller is the source of process control it is the clear choice. For installations where the PLC, including our AM-2300, is the source of process control direct output probes make a compelling choice.