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Troubleshooting Teleflex Fogging of Gauges

Technical Reference Manual

Fogging of Instruments

Until the introduction of Teleflex fog resistant gauges, all commercially available gauges were subject to fogging. Teleflex Pro Series gauges include a coating on the inside of the lens that prevents condensation from forming. Depending on the outside temperature, humidity, air flow to the gauge, and gauge placement in a panel, other gauges can fog. Usually the gauge fogs when the inside and outside temperatures of a gauge change drastically. Such a change occurs when the gauge is first turned on. The meter movement of the gauge heats the moist air inside while air outside the glass remains cooler, and the gauge fogs.

If the gauge is mounted vertically in a panel, the fog rises to the top of the gauge with little fog on the glass. If the gauge were horizontal, the fog would rise to the glass, probably covering it entirely. If the gauge were tilted back 45 degrees, only about half the glass would be fogged.

Fogging is dissipated when the heat inside the gauge causes an air convection to begin moving from the back of the gauge through its interior.

This constant flow of air should slowly clear the glass. Turning on the gauge light (causing more heat) helps in clearing the glass. If the glass does not clear, remove the socket and bulb and let a lot of air into the gauge. This step may be necessary in high humidity conditions. If air flow behind the gauge is poor (area sealed off), it may be more difficult to dissipate the fog. Replacing the fogging gauge is a last resort. It is not always an effective remedy, unless the replacement is a Pro Series unit.

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