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Replacing GLI, Signet & Other Sensors with Hanna Instruments Industrial Probes
Depending upon the model and manufacturer of the pH controller which is being used, one of the Hanna Instruments industrial pH or ORP electrodes can be substituted without any problem. Longer service life, lower cost, and faster deliveries are all reasons to make the switch. Since Hanna makes many different models for various applications, we should consider several factors to determine which electrode to use.
1. Distance from probe to controller
2. Required thermal sensor
3. Five wire differential versus two wire combination probes
4. Temperature of liquid measured
5. End connections
6. Matching pin (solution ground)
7. Attachment method
Most electrodes deliver a signal using a high impedance cable over a range limited to 45 feet. For longer distances, the signal must be amplified or converted to an analog form (4-20mA). The easiest method is to use a pre-amplifier. These devices can be battery powered or powered from the controller itself with a DC power supply. The Hanna HI 504-AMP preamplifier is battery powered with an internal battery which will last about five years. The male BNC end accepts the BNC connector from a standard electrode. The other end has a female BNC which can be attached to a wired connector using a male by male BNC adaptor or a male bulkhead fitting which in turn has an extension wire to the controller. Once this has been done, these parts can be a permanent part of the system. A second option is to connect the probe to an analog transmitter. The controller however must be able to accept this type of signal (4-20mA). Only a few manufacturers have controllers which allow this type of an input. Therefore, the preamplifier is normally used. Obviously, another option is to move the controller closer to the tank which is being measured. Then it becomes easier to calibrate the electrode and the cable length can be either 15 or 30 feet. Hanna probes are available in a variety of cable lengths. The standard length is five meters (15+ feet). Hanna probes with longer cables (15 meters or more) contain built in amplifiers.
Some applications require temperature compensation in order to provide an accurate reading of pH. ORP electrodes however, do not require temperature compensation at all. Some controller manufacturers try to prevent users from using other probes by using a specialized temperature sensor (even ORP probes can have a temperature sensor although it has no function). A common one is a “Balco 3K” sensor. To eliminate this problem simply install a 3000 ohm resistor across the required terminals. The most common thermal probes are the platinum RTD sensors. Hanna probes can be ordered with either a Pt 100 or a Pt 1000 RTD temperature sensor.
Differential probes (sometimes referred to as five wire) are very expensive to replace. This type of electrode is not really specified by the number of wires. In the case of a standard combination electrode with temperature compensation, the probe could have up to seven wires. The most common differential pH electrode made by Great Lakes is the model 6028. Standard combination probes either with or without temperature compensation can be used in lieu of a differential probe if the controller is able to accept either type of sensor. If the user has a GLI model P33 or P53 controller, it can be programmed to use either type of electrode. However, the GLI P63 (now discontinued) will not allow switching without a hardware replacement. Check with the user manual before committing to a replacement. Typically, one should order a probe with Pt 1000 temperature compensation. Hanna offers a replacement probe which will provide significant cost savings.
Although most probes use very generic glass sensors, Hanna industrial probes can be ordered with special flat glass ends. The type of glass used will extend the life of the electrode if it is subject to either high temperatures, low temperatures or fluoride ions. The use of special glass ends will also result in a probe which is more responsive. And because all of the Hanna industrial series probes have flat glass tips, the concerns about abrasion or breakage from stirred tanks or in-line applications become minimized.
Hanna industrial probes can be ordered with either the classic BNC ends or wire ends depending upon the terminal blocks used for the controller. That flexibility allows these electrodes to be used with a wide variety of controllers.
Some electrodes have an extra wire which is used to shunt electrical voltages present in a tank away from the internal electrode parts. This is commonly referred to a solution grounding using a matching pin on the end of the electrode. Some applications where this is a problem will severely shorten the life of an electrode unless this technology is employed. Fortunately, all of the Hanna industrial series 1000/2000 have this feature as standard. Some controllers are equipped with terminal connections for this purpose. All of the Hanna controllers are designed to take advantage of this technology. We have seen probe life extended by months when users have switched the controllers or transmitters without this feature to one of the Hanna advanced controllers. We highly recommend the use of this technology.
And finally, the Hanna industrial electrodes are constructed with a PVDF body for the best chemical resistance. At each end of the sensor, ¾” NPT connections are provided. If a larger probe was in use, a simple bushing will allow the installation of the Hanna probe. For submersion into a tank, a schedule 80 PVC pipe may be used. We recommend the use of RTV compound on the threads to prevent leaking as opposed to Teflon tape.
If you have any questions regarding the use of Hanna probes with your current equipment, please call MBH Engineering Systems for assistance. We will be happy to assess your requirements. All of the Hanna industrial probes are in stock for immediate delivery. We also stock all of the necessary calibration, cleaning and storage solutions.
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