How to understand the concept of range in intelligent transmitters

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Since smart transmitters are capable of handling both analog and digital signals, their methods of tuning and calibration differ from those of conventional transmitters. Regardless of the method used for calibration, range considerations are always involved. The various terms used to describe the range in smart transmitters can lead to confusion among some instrument technicians regarding this concept. This article outlines some of the concepts related to the range of smart transmitters, thereby facilitating their proper calibration. http://yunrun.com.cn/upload/201605/30/201605301831117808.jpg Monocrystalline silicon transmitter. Original source: yunrun.com.cn/tech/551.html There are six terms used to describe the measurement range in smart transmitters, namely: 1. The lower limit of the variable value of the smart transmitter, abbreviated as VLL; this can be understood as the lower limit of the transmitter’s maximum measurement range ； 2. The upper limit of the variable for intelligent transmitters, abbreviated as VUL, can be understood as the upper limit of the transmitter’s maximum measurement range. 3. The sensor lower limit, abbreviated as LSL, can be understood as the lower limit of the range for which the transmitter is actually used in operation ； 4. The sensor upper limit, abbreviated as IJSL, can be understood as the upper range for which the transmitter is actually used in orders. 5. The lower range limit of the intelligent transmitter, abbreviated as LRV, can be understood as the lower range limit required for control and display ； 6. The upper range limit of the intelligent transmitter, abbreviated as URV, can be understood as the upper range limit required for control and display. To help everyone understand, here are two examples. Fault inspection and handling of safety barriers: yunrun.com.cn/tech/1991.html Example 1: Range specification of single-crystal silicon pressure transmitters. For a pressure transmitter with a range of 0–1.6–16 MPa, the lower limit of the variable value is VLL = 0 MPa, while the upper limit is VUL = 16 MPa. However, it is not possible to measure such a wide range of pressures in the actual usage environment; therefore, the pressure measurement range should be selected based on the equipment. For example, if a pressure range of 0–2.5 MPa is used, then the lower limit LSL of the sensor is 0 MPa, and the upper limit USL is 2.5 MPa. To ensure that a pressure range of 0–2.5 MPa corresponds to an output of 4–20 mA, the lower range limit LRV is 0 MPa, and the upper range limit URV is 2.5 MPa. Example 2: Range specification of a temperature transmitter. A thermocouple temperature transmitter equipped with a K-type thermocouple has, per standards, a calibration range of -200～1300°C; therefore, the lower limit of the variable value for this transmitter is VLL = -200°C, and the upper limit is VUL = 1300°C. However, it is not possible to use such a wide temperature measurement range in the actual application site; therefore, the thermocouple should be selected based on the specific conditions there. For example, if a thermocouple with a range of 0–1100°C is used with that transmitter, then the lower limit of the sensor’s measurement range LSL will be 0°C, and the upper limit USL will be 1100°C. To ensure that 0–600°C corresponds to a signal of 4–20mA during use, the lower range limit LRV is 0°C, and the upper range limit URV is 600°C. In the digital signal processing section, its variable range is from VLL to VUL, and this range remains unchanged after the transmitter is designed. When assembling the transmitter and sensor, the LSL and USL must be set within the instrument. When the signal exceeds the LSL, USL, or VLL, VUL, the instrument will give an alarm in the prescribed manner. The setting of LSL, USL, VLL, and VUL is done by the intelligent transmitter manufacturer; users do not need to do it. Author: Huang Wenxin