What is a Differential pH probe?
There are hundreds of manufacturers of pH (or ORP) probes, some traditional probes priced so low as $100. Our differential pH probes cost more than six times that much. It doesn’t take a math degree to realize you would have to utilize six or more traditional probes to justify buying just one of our Aquametrix differential pH probes. Have you ever bought a $99 printer only to find that you spend that much every month just for the ink? Then you understand that the initial cost can be very different from the total cost of ownership. So, let’s talk total cost of ownership. AquaMetrix has a 60-year history of building sensors and controllers for the most challenging environments. This includes industrial wastewater, municipal wastewater, HVAC and aquaculture. We manufacture and supply pH probes to these industries simply because:
- They work well
- They save money
Let’s see how we can make such a bold claim as “saving money.” Can we really claim that one AquaMetrix differential pH probe will outlast six of the other guys? Well…yes. Most traditional pH probes are classified as ‘combination’ probes. Combination probes are named such because the reference electrode and process electrode are “combined” into one glass or plastic body. A typical combination probe may last for two years in clean water, but it will be blessed if it lasts 6 months in a moderately challenging environment, like wastewater. That’s a cost of about $200/year. Typically, the things that kills a typical combination pH probe include contamination of the reference solution, poisoning of the reference electrode or plugging of the liquid junction.
In contrast, a differential pH probe replaces the bare silver wire that serves as a reference electrode with a completely enclosed glass electrode identical to the process (measuring) electrode. This means it can’t be poisoned. The liquid junction, a tiny porous structure that allows current to flow from the process to the measuring electrode, is replaced by a big, beefy, replaceable salt bridge. This means that, when the junction gets plugged up, you can just throw it away and screw in a new one. It also means when the reference solution becomes contaminated within the process, you can simply:
- Unscrew the salt bridge
- Pour out the old solution
- Add new solution.
But wait, it gets better! Remember, that in a combination probe, the reference electrode and the process electrode are “combined” into one complete circuit. So, when a stray voltage from, say, a ground loop, finds its way into the process it messes up the exposed reference electrode (a bare silver wire coated with silver chloride). However, a differential probe uses two identical electrodes—both sealed in glass and immersed in a salt solution—and each is connected to a ground rod to make two half-circuits. When a stray voltage creeps into the process it goes straight to the ground rod and is subtracted from both electrodes. See the schematic below. So, no faulty readings. No ground loops. Additionally, the differential probe has an embedded pre-amplifier. This means instead of being restricted to a 15-foot length cable typical of a combination probe, the cable of an AquaMetrix probe can be 1000 feet or longer.
It should come as no surprise that, not only will an AquaMetrix differential probe outlast more than six combination probes in a challenging environment, but it will also work more reliably. That part alone can save you a lot of money and headaches!
To find out more about AquaMetrix differential pH or any of our other probes contact Brian Gannon at bgannon@wateranalytics.net