Did you know there is a hidden current that could be eating your submersible pressure transducer alive? This can happen even as your submersible performs admirably – until one day it dies suddenly and you uncover a ghastly scene of corroded metal. Don’t worry, though. We’ll show you how to find it and stop it before it stops you!
Before we go any further, we have to start by facing one unmistakable fact:
Submersible Pressure Transducers Are Submerged
Why state the obvious? Because it’s critical to our understanding this sneaky hidden current and all its underhanded ways. By nature of being submerged, a submersible pressure transducer is often grounded. That’s because the sensor is case grounded, and the liquid will likely carry a current (unless, of course, its distilled water), connecting the case ground to earth.
This secret ground is very important. If unrecognized, you can inadvertently kill your sensor and expose your electronics to electrical noise and surge damage. You get in trouble if you forget this rule:
Don’t Connect The Drain Wire To Ground At The Box
It’s a rule that likes to be broken. However, if you break this one, you’ll be playing into the hand of the surreptitious hidden ground. You see, what it wants is a ground loop so it can subject your circuit to the dangers of electrical noise and electrolysis.
Electrical noise is a common issue that occurs either when your shield and drain wire are not properly grounded, when you have exposed flying leads, or when you have a ground loop.
In the case of a ground loop on a submersible pressure transducer, the current in the drain wire is flowing from one ground to the other due to the difference in potential between the two grounds. As the current flows back into the drain wire on the receiving end, the current can be induced onto the signal wire. This can either add to the signal, causing an inaccurate reading, or totally overpower it resulting in a loss of signal.
Electrolysis, on the other hand, is a more silent killer. In this case, your submersible pressure transducer is acting like an electrode sitting in an electrolyte solution (again, unless your monitoring distilled water, your liquid is probably full of conductive minerals). As the current flows through the liquid, it dissolves the metal housing of your sensor, eating it alive.
Disconnecting the drain wire in the control box can solve both of these issues. However, the goal is to discover the problem before it occurs, stopping the hidden ground loop before it can begin. Think of this as:
The Preemptive Strike
Testing the presence of a ground loop can prevent the problem before it starts. Even better, this is a very easy test that takes only a few seconds to complete. Simply grab an ammeter or a voltmeter and place it between the drain wire and the ground in your control box. If there is voltage, you have a ground loop – in which case you would not connect the drain wire.
A ground loop will only exist if there is a difference of potential voltage between two grounds. In other words, having two grounds is fine if they have the same potential. It is the difference in potential that causes the flow of electrons. It creates a battery on your grounded wires, which is detectible and preventable.
If you fail to test for a ground loop (and you have one), you’ll expose your circuit to all kinds of nasty electrical noise and potential electrolysis. Even worse, you could cause an unstable circuit that would fail to protect you and your electronics from short circuits, power surges, and lightning strikes.
So think like a US General and get preemptive (or preventative, whichever you prefer) on your wiring practices. Find those devious ground loops before they destroy your submersible pressure transducer and mess up your signal!
And of course, call us. We can help you understand what’s going on if you have troubles. We can help you with your brand new submersible pressure transducer as well ;)
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