HI 21211-1 - pH Controller, 2 SP, ON/ OFF Control & Analog Output - 230 VAC * Simple to operate * Computer compatability * Fully programmable with back-up power supply The HI 21 controllers are simple-tooperate, 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. Some HI 21 models are equipped with a bi-directional RS485 port, which allows remote control of the instrument from a PC. Push button password programming prevents tampering. The microprocessor memory is fully programmable and has a 3 month backup power supply. The Fail Safe Alarm system protects the HI 21 against the pitfalls of process control, like power interruption or line failure. With HI 21 quick 1, 2 or 3 point calibration at pH 4.01, 7.01 and 10.01 comes standard. The temperature can be manually or automatically compensated for. You can also choose from ON/ OFF, Proportional and PID control to save on chemicals. Each HI 21 model is supplied complete with instructions.