Proper Installation of a Gauge
Installation for Visibility
When possible, pressure instrumentation should be installed in visible, readily accessible locations. Readouts should be located at eye elevation. Headroom should be provided for instrument removal, as well as any space for tools and test equipment that might be needed (Moerman, 2013b).
Measures to Eliminate Temperature Effects
Ambient temperatures above or under the specific acceptable temperature operating range of the gauge (due respectively to the vicinity of a source of heat or cold) must be avoided. The external housing must be checked for sufficient temperature decoupling from the process or utility system, as gauges may be affected by the temperature of the fluids flowing within the process or utility system. If the process/utility system or lines become too warm, the effects of changes in process fluid temperatures can be minimized by means of a cooling element (Fig. 7.78), a diaphragm seal with capillary tubing for remote mounting, a siphon, a loop seal or by purging. Loop seals and siphons are less hygienic solutions. Alternatively, the gauge housing can be
FIGURE 7.77 Hygienically designed electronic pressure measurement devices with stainless steel or plastic housing. The external housing and wiring may not collect dust or soil, requiring a design with smooth transitions and free from pockets. To be self-draining the instrument housing can be made with a sloped top surface, although it is possible to install pressure measurement devices with angles of more than 30 degrees from the vertical. Courtesy of Endress + Hauser AG.
cooled electrically (Peltier effect) or by means of water. If the process/utility system or lines have become too cold, sensor heaters may keep the sensor at elevated temperature (typically 40—80°C). If there is downward temperature drift due to the process/utility system being frozen, freeze protection may occur by means of steam tracing or resistance heating (electronic compensation) in combination with thermal insulation. If a diaphragm seal is used, the oil filling in the diaphragm seal housing not only may prevent humid ambient air to enter the gauge but it also may prevent a cold process/utility fluid from freezing any condensate within the gauge (Moerman, 2013b).
FIGURE 7.78 Changes in ambient temperature around the measurement system due to high process/utility temperatures can be minimized by means of a cooling element mounted between the gauge and the hot pro- cess/utility system. Courtesy of
Endress 1 Hauser AG.