Difference between photohelic and magnahelic guage?

Answer 1

PHOTOHELIC® Pressure ControlPHOTOHELIC® models combine the MAGNEHELIC®gauge with a precise pressure switch that lets you control low and high gas pressures. Knob controls adjust dual set points, which allow for variable deadband control. These set points contain photocells that actuate DPDT relays when room pressures reach a preset upper or lower limit, and they can be set up to control corrective damper action. As the room pressure changes in response to damper motion, and the indicator returns to the null band, damper motion is halted.

Answer 2

Photohelic gauges measure pressure using a diaphragm mechanism that converts pressure into a measurable signal. Magnahelic gauges use a magnetic mechanism to measure pressure differentials across two points. Both gauges can display the pressure readings on a dial or digital display.