Level Alarms for liquids that coat, crystallize, or foul other sensors.
The capacitive sensor is encased in a polypropylene pipe with flat end. The sensor is completely protected from the process liquid.
The capacitance versions of our alarms have the same features as our float switch version, (because they use the same PCBs) which means a loud buzzer and a snooze alarm feature where the buzzer sounds again in 30 minutes if the alarm is not corrected. Or alternatively, the button can just shut if off. (see operating instructions for details on the possible modes)
As with our float-switch based level controllers, installation involves just mounting the alarm on your tank and plugging in the power cord. The orientation is specified when ordering, but if you want to change it, it can be switched from high level to low level with a switch inside the enclosure. There is nothing to calibrate of adjust.
There is is nothing to wear out and no moving parts to limit the lifetime of a capacitance sensor. As for physical maintenance of the probe tip, occasional cleaning off the sensor tip may be required depending on your conditions. The sensor tip can tolerate a tremendous amount of buildup, but there is a limit – it should be cleaned if the buildup is approaching ½” thickness. The sensor will still function beyond this but at some point of buildup, the liquid will be so far from the sensor that it will be unable to detect it. If cleaning is necessary, it is done quite easily as the glass is smooth and easy to clean.
COATING AND FOULING LIQUIDS
This is the tank alarm for difficult liquids that foul, coat, or crystallize on other types of sensors. Capacitive sensing easily tolerates thick deposits of dirt, sludge, viscoes coatings, or crystallization.
BEST FOR LIQUIDS THAT COAT
There are other ways to sense fouling liquids such as conductivity probes, ultrasonics, optical sensors, photo-electrics, and thermal dispersion. Below is why we think capacitance is the best choice for fouling liquids.
Conductivity probes are susceptible to buildup onto the probes which will render them non-conductive, and therefore useless, in no-time. They have their uses, and we use them too, but not for dirty liquids.
Ultrasonic sensors are good for gauging level continuously, but they have to be programmed to the tank depth, dead-zone, and alarm points. Every time you want to adjust the anything, you need to connect a computer! In addition, they are very prone to errors from turbulence and foam, floating debris. Further, they have a dead-zone requirement of a couple of feet where nothing can be sensed. If they “miss” the liquid rising past the programmed level point and into the dead-zone, then there is no alarm! Especially bad for high level alarms. Finally, they must be placed far away from the tank wall, or else in a dedicated cylinder – really unsuitable for plating tanks where space is limited.
Optical sensors and photo-electric sensors both suffer from the same problem: if the lens gets coated, they don’t work. This unreliability makes it a no-go for us.
Thermal dispersion sensors can also be fouled: they tolerate more coating than optical sensors, but once the surface is coated thick enough, then you no longer have a functioning sensor.
Capacitance sensors, by design, sense through coatings up to 15 mm thick! have no moving parts to break, and nothing to wear out.
HOW CAPACITANCE SENSORS WORK
Capacitance sensors work by generating a capacitance field some distance away from the sensor with co-centric oscillating plates. If anything with a dielectric constant different that air enters this electrostatic field, it changes the capacitance of the internal oscillator and the medium – evey solids – is sensed. The more the dielectric constant differs from air, the greater the sensing range. Basically any conductive water-based liquids will be easily detected, whereas dry materials like plastics, will not. This table of dielectric constants for various materials gives a long list of materials. The maximum extent of this sensing field in our sensors is 17 mm distance. So it is actually possible to use this as a non-contact sensor. However in practice we find its better to shorten the field so the alarm stops sensing even when there is a thin residue of liquid clinging to the sensor tip.
These are also a great choice for viscous liquids like epoxy resins. A separate page on the capacitance sensor used with viscous liquids is here.
CAPACITANCE LEVEL ALARM
Polypropylene Pipe $358
CAPACITANCE LEVEL ALARM
Kynar Pipe from $458
Choose either a relay output or dry contact. The relay output is 15A@120VAC using a 10ft piggyback cord. Alternately, a dry contact is provided through a 10ft rubber-jacketed cord with four conductors. (two for 120VAC, and two for the output) Instructions here
Extra cable length over the standard length. Heavy 0.032″ jacket for superior durability, Stranded conductors x 24 gage.