31570 6-Inch Photojet Edge Guide Sensor

The Model 31570 Dynaguide Centerguide Sensor includes two 6-inch Photojet centerguide sensors. These sensing heads consist of a light source and photo-conductive cells. The light source is a 6-watt tubular fluorescent lamp that operates on 115 volts AC, 50/60 Hz. 

The photoconductive cell is a cadmium sulfide strip 6 inches long. Its resistance varies with the amount of light falling on it. A pair of adjustable shutters in each photocell housing provides for electrically balancing the sensing heads on each side of the web.

The sensors are used with the Model 33130D Digital Amplifier, in which the sensors resistive web position signals are converted to a voltage signal to operate the moving coil of an electrohydraulic controller. The sensors photocells are supplied with a low-level (15V) DC voltage, this insures a long service life. The amplifier also contains an output voltmeter to aid in initial set-up and for continuous monitoring of sensors during operation. 

Power input to the amplifier is 115 volts AC (± 10%), 50/60 Hz, 70 VA. 

Principle of Operation
Resistance of the photoconductive cell varies, depending on the amount of light falling on it. The cells are placed in opposite legs of a bridge circuit with the input of the amplifier so connected to the bridge to act as a null detector. 

When the web is centered, the resistance to both photocells is equal, therefore, the input voltage signal to the amplifier from the bridge is zero and no output to the moving coil. Lateral movement of web causes resistance of one cell to increase and thereby unbalancing the bridge. This produces voltage to the amplifier. The output of the amplifier is proportional to the input voltage, this will cause the electrohydraulic controller to initiate the corrective movement to correct the deviation.