Tech Tip: DrDAQ as pH alarm

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Q. I want to use the output from the pH probe on the DrDAQ to turn a pump on when the pH exceeds a set value. Is there software available or some info on using the output pins to control a solid-state relay?

A. Yes, you can do this using the PicoLog application supplied with your DrDAQ. The Edit channel > Parameter options dialog has an Alarm button: click this, enable the alarm, set the lower and upper thresholds, and PicoLog will activate an alarm sound when the pH goes out of range. Now check one of the relevant Digital Output boxes to make PicoLog activate the desired output at the same time as the sound. The outputs are nominally 0 volts low, 3.3 volts high, with 2.2 kΩ source impedance, suitable for driving an NPN transistor or a solid-state relay. 01-2016