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The ORP90 is a Cadmium Sulphide photoconductive cell. Basically a light dependent resistor with the incident light arriving aligned with pin 4. The data sheet describes the target application as flame control and ignition detection.

The side view shows the support structure. The maximum voltage across the resistor can be 300 Volts and the dissipation is 1 Watt maximum at 25 °C falling to 0.3W at 70°C. The more usual operating voltage would be 10 Volts. The dark current is given as 2.5 μV. The device is most sensitive to red light and at a colour temperature of 1500°C is twice as sensitive as when illuminated by a Tungsten filament lamp at 2700°C.

The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 54 mm tall.

Reference: Data-sheet. Type ORP90 was first introduced in 1958. See also 1958 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.