INSTALLATION
Page 21
MANUAL
CT
Controllers
WATER
CHEMISTRY SENSORS
Sensor Design
The pH and ORP sensors are non-corroding sealed
combination electrodes (Figure 9). They do not require
refilling. Each sensor has an external plastic body and an
inner glass tube which can be broken if stressed too severely.
The potentiometric sensors produce small voltages - in the
millivolts range. Since they have a high impedance (20 to 50
megohms), the electrical current produced by the sensors is
extremely small - in the picoamp (10
-9
A) range. The output is
so small that it cannot be measured with ordinary voltmeters
and must be internally amplified by the controller.
There is no electrical current flowing from the controller to the
sensors and the sensors are optically isolated from the high
voltage circuit inside the electronic module. Therefore they
create no electrical danger.
pH Sensor
The pH Sensor senses the acidity of the water and works with
any acid or base. It is recognized by its blue color and the
glass bulb at the tip.
ORP Sensor
The ORP (Oxidation-Reduction Potential or Redox) Sensor
monitors the activity of the sanitizer (Fast Acting Free Chlorine,
Bromine or Ozone) through its oxidizing power. It is
recognized by its red color, the wide platinum band at the tip of
the electrode and the white plastic tag on the cable.
Sensor Installation
The pH and ORP sensors are shipped in individual cartons for
extra protection. When ready for installation, remove the
plastic cap on the tip of the sensor. If it is difficult to remove,
dip it in water for a few seconds. It should then slide off easily.
There may be a white crystalline deposit around the cap. This
is produced by the salt solution used for shipping and does not
affect the performance of the sensor.
For installation of a sensor, the 3/4" bottom part of the Fast &
Tite fitting should first be screwed in the PVC Tee (Figure 6).
Teflon tape can be used but it should not be overtightened.
The sensor with the upper part of the fitting should then be
carefully inserted, as shown on the schematic above, being
careful not to bend or overtighten it, to avoid breaking the small
glass tube inside. The sensor tip should be about ½" (1 cm)
inside the PVC tee. It does not matter which sensor, ORP or
pH, is upstream or downstream.
Sensor Cables
Each potentiometric sensor is supplied with a standard 10' (3
m)-long cable made of coaxial wire designed to minimize
electrical interference. For ease of identification, all ORP
cables have a white marker.
Figure 19 - ORP and pH Sensors
The cables are terminated with bayonet-type, spring-loaded,
push-and-twist male BNC connectors. These are connected to
the proper female BNC connectors located on the left side of
the controller cabinet.
If the cable is longer than needed, it should be coiled neatly
and attached under the cabinet. DO NOT CUT THE SENSOR
CABLE under any circumstance.
If a longer cable is needed, custom-made extension cables
with BNC connectors can be ordered from the factory in
lengths of up to 100 feet. For longer distances, a pre-amplifier
may be required. Consult your dealer or the factory for details.
Electrical Interference
Electrical interference from high voltage equipment, such as
power transformers, pumps or high voltage lines, may
sometimes produce erratic readings from the sensors. It may
then be necessary to insulate the sensor cables by mounting
them inside a metallic conduit line that is properly grounded.
Small signals may also be picked up from current leakage
through the water line, due to faulty wiring or improper
grounding of equipment, such as a pump or heater.
Electrolytic chlorine generators are also a frequent source of
current leakage.
To check for current leakage, compare the readings of the
sensors when they are in line and when they are dipped in a
plastic bucket containing the same water from the tower basin.
If you get different readings, there is current leakage. Its
source must be identified and eliminated with proper grounding
by a qualified electrician.