Hanna Instruments Multiparameter Digital Ph, ORP, Temperature Probe

The HI1036-18xx is a digital combined probe that measures pH, ORP, and temperature. This probe also incorporates a potential matching pin. The matching pin is considered the "earth ground" connection and is used to prevent ground loop effects from
causing erratic readings and damage to the system. The pH glass has been chosen to produce stable quick equilibration
even in low conductivity waters. Additionally, the pH sensor is designed to produce a mV value near pH 4 (not pH 7 like typical pH sensors) should it stop working. A broken pH electrode that produces a mV value near pH 7 would produce an alarm state and
disable any pump activated. The ORP sensing surface is a large smooth surfaced platinum band that encircles the circumference of the
temperature probe. It is referenced to Ag/AgCl reference electrode (3.5M KCl). The ORP and pH sensors and reference electrode use a differential measurement technique which is known to stay in service and provide accurate measurements under adverse conditions that may cause conventional pH probes to produce erroneous measurements. The HI1036-18xx probe with its differential amplifiers greatly reduces inaccuracies caused by ground loops which may exist between process and instrument grounds. With the differential technique, a ground loop current will flow through the low impedance path of the matching pin thus providing immunity to the measurement signals.
Additionally the probe converts these measurements to a digital signal to eliminate noise and static due to high impedance signals carried by cable. 
 
The HI1036-18xx with the BL120 or BL121 pool controller helps to promote the health and safety of pool and spa water.