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1. Why is it necessary to choose a location with a relatively constant ambient temperature when installing flange transmitters? Unlike ordinary transmitters, a flanged transmitter has its capillary and flanged diaphragm box as a sealed system, functioning like a large thermowell. When the surrounding environment changes, the filling fluid within the system expands or contracts, thereby causing pressure changes in the system. These pressure changes act on the sensitive elements of the transmitter, resulting in additional errors in the instrument readings. In ordinary transmitters, the pressure guiding tube is not a sealed system; pressure changes due to temperature variations, and the medium can diffuse into the process flow, thus not affecting the instrument’s output. When installing flanged transmitters, make sure that the transmitter and the flanged diaphragm system are not exposed to direct sunlight, to avoid drastic changes in ambient temperature caused by exposure to the sun. Additionally, the two capillaries of the differential pressure transmitter should be at the same ambient temperature, so that temperature changes within a certain range can cancel each other out. 2. Why are flange transmitters for high temperature and high vacuum particularly expensive? The flange diaphragm of a flange transmitter is in direct contact with the medium, which means that such transmitters can easily operate under high-vacuum conditions. When the flange transmitter operates in a vacuum environment, an outward pulling force acts on the isolation diaphragm; as a result, the diaphragm bulges outward, increasing the volume of the transmitter’s sealed system. This leads to a decrease in pressure within the filling fluid, creating a vacuum condition. At this time, external gases may penetrate into the diaphragm box through the welds and joints, causing gas to be present in the filling fluid and thus affecting the performance of the instrument. In a flanged transmitter, the boiling point of the filling liquid decreases as pressure drops. If the flanged transmitter operates under negative pressure, a vacuum will form within the sealed system, which in turn lowers the boiling point of the filling liquid and causes it to vaporize. If the temperature of the medium drops below the boiling point of the filling fluid, vaporization occurs. If the medium temperature is much higher than the boiling point of the filling fluid, the vapor pressure of the filling fluid will be very high. This not only exerts pressure on the sensor element of the transmitter, causing measurement errors, but also causes the diaphragm to bulge outward, resulting in its permanent deformation. When the transmitter operates under conditions of high temperature and high vacuum, the filling fluid is in a condition where it vaporizes very easily. To this end, the manufacturer must treat such transmitters in a special manner: the filling liquid used in the diaphragm box must be high-temperature silicone oil, and the amount of filling must be controlled precisely – neither too much nor too little. Any gas present in the silicone oil must be completely removed before filling, and the diaphragm box must be evacuated to an absolute vacuum with no residual pressure left. The welding of the diaphragm box must also be absolutely secure. All of this increases the processing workload and cost of the transmitter, which is why flanged transmitters for high temperature and high vacuum environments are particularly expensive. 3. What are the differences between Rosemount 3051C and Yokogawa EJA sensors? The sensor of the Rosemount 3051C intelligent transmitter is a silicon capacitive type; it converts the parameter being measured into a change in capacitance, and the differential pressure or pressure being measured is then determined by measuring this capacitance change. The sensor of the Yokogawa EJA intelligent transmitter is of the silicon resonator type; it converts the parameter to be measured into the vibration frequency of a silicon beam, and the measured differential pressure or pressure value is obtained by detecting this frequency.