PH500121-1 pH Digital Controller with Matching Pin, Analog Output, 115V by Hanna Instruments pH 500 series of controllers are simple to operate, microprocessor-based process meters packed with features. For more flexibility and better resolution for chart recorders, any two points between 0 and 14 pH can be chosen to correspond to the analog output spans. Several pH 500 models are equipped with a bi-directional RS232 port. Push button password programming prevents tampering. The Fail Safe Alarm System protects the pH 500 against the pitfalls of process control, like power interruption or line failure. With pH 500 quick one, two or three point calibration at pH 4.01, 7.01 and 10.01 comes standard. The temperature can be manually or automatically compensated for. Models with RS232 output allow computer compatibility, a necessity for process control instrumentation. You can also choose from ON/ OFF or proportional dosage to save on chemicals.