Turtle Tough pH/ORP Sensors have been engineered for installation into industrial processes. It is the responsibility of the end-user to ensure that the process conditions are within the specifications of the sensor to obtain optimal sensor life.
Types of Installation
When installing care should be taken to avoid any moisture ingress through the cable inlet/outlet. For fully submersible installations adequate waterproofing options must be selected at the time of order. Alternatively, you can provide your own waterproofing method by using a fully sealed immersion rod with adequate sealing applied to the sensor thread (ie with thread sealing tape), ensuring that process liquid cannot sit on the backend of the sensor.
It is recommended that immersion rods be made from stainless steel or a suitable metal product to provide adequate earthing for the sensor. Plastic immersion rods are very susceptible to static and provide no grounding to relieve the sensor of any stray current in the process environment. Sensors will often produce "jumpy" or erratic results if not properly grounded.
Never suspend the sensor by the cable as this will cause damage to the backend connections within the sensor. If such an installation method is required, the cable protection (CP) option should be invoked. Cable protection uses vinyl or norprene sheath around the cable which is fixed to the body of the sensor thus providing the required strain relief, allowing the sensor to be raised or lowered by the cable. It also provides additional protection from the environment, protecting the cable from accidental damage from sharp, hot or abrasive materials which compromise its integrity. Please note that cable protection only ever covers 2/3rds of the sensor cable length.
All pH/ORP sensors can be installed in-line and the correct inline method should be chosen at the time of order. For inline installation, please pay attention to the following:
- Where possible, avoid using front end threaded connections. When threading the sensor in/out of the process continuously (ie each time you clean and calibrate) the cable is constantly exposed to stresses from twisting. This constant twisting and curling of the cable can damage the connections in the backend of the sensor. It is recommended to use either twist lock, sanitary or hot-tap installation methods.
- Both twist lock and sanitary tri-clamp installation methods require isolation of the process line for insertion and removal. Hot-tap is the only method that allows insertion and removal while the line is live.
- All inline sensors have their temperature compensation (TC) element located at the tip of the sensor for accurate process temperature measurement. This does expose the element to potential damage, so for sensors ordered as fully submersible, they have their TC located in the backend of the sensor for better protection. In circumstances where you want to use a submersible sensor for an inline installation, it's important to note that the TC is sitting in "ambient" conditions and will not accurately represent the process liquid unless that liquid is also at ambient temperature.
- Where possible avoid plastic pipework. Static and stray current can produce very erratic readings. If you do have plastic pipework, sensors should be installed in metallic housings that can be adequately earthed, or you must have some other means of adequately earthing your pipework.
Earthing and the Electrical Environment
It is important that ALL electrical equipment is properly earthed and that sensors are installed in adequate earthed environments. As such it is recommended that pH/ORP sensors are installed in metallic fittings that can be properly grounded. pH and ORP sensors measure small incremental millivolts (ie there are just 59mV per pH unit), so any small amount of current, static or otherwise can cause large shifts to the sensors readings. In these instances, there is nothing wrong with the sensor; it can only see what it sees. Instead, the cause of the stray current must be eliminated. Stray currents are usually caused by improperly earthed or shielded equipment. They can occur on either the process side of the power/electrical side and they can even occur through the atmosphere/air. As such the pH/ORP sensor should be installed as far away as possible from high current carrying equipment such as pumps, motors, variable speed drives etc.
It is recommended that pH Sensors be optimally installed at a 45° angle as this avoids air bubbles being trapped at the sensor/process interface and ensures optimal glass/silver-chloride interaction. It is also acceptable to install vertically down. pH sensors should never be installed inverted (ie upside down) or below the horizontal axis. They must be at least 15° above the horizontal axis.
Position Insensitive Sensors
For ORP and Conductivity, these are both positions insensitive, meaning the sensor can be installed at any angle. pH and Dissolved Oxygen on the other hand are not, and must always be in the vertically down position.
It is still recommended to install these sensors vertically down (tip down) for several good reasons:
- Upside down is messy and can result in product spillage and overflow.
- It can be unsafe if the process is not isolated correctly.
- Product with any solids… solids can settle out and get trapped in the sensor tip and cause excess fouling.
- People see an ORP or Conductivity sensor upside…. They then install a pH or DO sensor upside down (which is not good).
Choosing the correct waterproofing option.
Recommendations for Inline, Immersion and Submersible Installations
Turtle Tough inline twist-lock sensors and immersion sensors are NOT intended to have rain or other continuous forms of water on the back of the cable. In this case, a shorting can result in a variety of anomalous failure modes.
** IF SUCH ANOMALOUS FAILURE MODES RELATED TO THIS OCCUR THIS IS CONSIDERED AN IMPROPER INSTALLATION ISSUE AND THUS NOT COVERED UNDER THE STANDARD ASTI WARRANTY **
The sealing on the back of a twist lock and immersion sensors is water-resistant, but not waterproof. The standard default isolation on the back of a sensor is a strain relief grommet. This allows for the sensor to be somewhat moved and for some minor water exposure without causing sensor failure. For more aggressive water exposure to the back of the sensor, additional precautions must be taken.
Inline Use -Indoor
Inline Use -IndoorIf a standard sensor (such as our immersion or twist-lock sensor series) is used for inline installations only (no immersion or submersible use is planned) then no special precautions are required if it is for indoor use. This assumes that the back of the sensor will not be exposed to corrosive gas present and/or the plant will not cause any process media to get onto the back of the sensor, nor give it significant water exposure by washing down the area.
Inline Use - Outdoor
If a standard sensor (such as an immersion or twist-lock sensor series) is used for inline installations only (no immersion or submersible use is planned) then there generally ARE special precautions required for outdoor inline use. The most common is to seal the back end of the sensor in conduit to isolate the back end of the sensor. The most common approach so to use sufficient TEFLON tape and an NPT coupling to create this back sensor seal, and then either a rigid or flexible conduit back to the transmitter where is the lead wires are terminated for cable isolation. This creates a barrier that makes the sensor suitable for conditions where rain and other outdoor elements could damage the seal on the back of the sensor. Specifically, this can prevent water from attacking along the sensor cable and causing internal shorting to solder joins inside the unit itself.
Another approach for sealing the back of the sensor if there will be significant water exposure is to add a waterproofing option. In general, for such cases, just the least expensive Cable Protection option is sufficient, with a 3/8"X1/2" vinyl tubing properly installed. The Cable Protection option has a slight surcharge for extended cable lengths. In some cases, the more robust Standard waterproofing option can also be used to fulfil this purpose. Unfortunately, waterproofing options cannot be added once a sensor has been fabricated but rather must be installed at the time of manufacture.
Immersion use is defined as when the sensor is immersed into the process media, but the entire sensor is not submersed. This means that the back of the sensor is NOT completely below the process media level. Immersion installations always require the back of the sensor/waterproofing to be sealed with a mating 1" FNPT coupling and the cable run in conduit. The Cable Protection or Standard waterproofing options can be added if desired/required to make the sensor life better even for such immersion installations. It is possible to use the standard immersion or twist-lock sensor for immersion use without adding a waterproofing option if VERY GOOD care is taken to seal the back of the sensor with a coupling and properly running the cable in conduit back to the transmitter.
Submersible UseSubmersible use is defined as when the sensor is COMPLETELY immersed into the process media (anywhere from 30cm below the fluid level too much much deeper). In this case, the entire sensor is submersed. This means that the back of the sensor IS completely below the process media level. Submersible installations always require the back of the sensor/waterproofing to be sealed with a mating NPT coupling and the cable run in conduit.
For an additional sealing option, a Standard waterproofing option can be added if desired/required. There is a special surcharge if the sensor has a longer cable length than the standard 3 metres for the Cable Protection and Extreme waterproofing options only. It is possible to use the standard immersion or twist-lock sensor for submersible use without adding a waterproofing option if very, very good care is taken to seal the back of the sensor with a coupling and properly run the cable in conduit back to the transmitter. The use of Standard or Extreme Waterproofing options is VERY STRONGLY recommended (although not strictly required) for submersible installations.
Last comments on waterproofing options
The waterproofing options offer nominal isolation to extreme isolation in the following order going from least isolating to most isolating:
Cable Protection << Standard Waterproofing <<Extreme Waterproofing
Most users will only ever require the Cable Protection, Standard Waterproofing or Extreme Waterproofing options but the more extreme version that supports the presence of oxidizing chemicals and organic solvents are provided for such customers. In general, the Extreme Waterproofing option is only really required for submersible type installations. Note that ONLY the Cable Protection and Extreme Waterproofing provide for COMPLETE cable isolation back to the transmitter.
If you should have any doubt about whether the exact sensor model that you are using is appropriate for the installation style that you are planning to implement, please contact the factory for further assistance.