Transmitter Technical Characteristics
With the development of science and technology, people have higher and higher requirements for transmitters, and their structural performance is also specified in more and more detail.The smart transmitters produced now have dozens of technical indicators.But for the user, it is neither possible nor necessary to verify the technical indicators of the transmitter on site, and some indicators will not change.However, understanding and mastering these properties is beneficial for the use and maintenance of the transmitter.
1. Measuring range, upper and lower limits and range
Each transmitter used for measurement has a measurement range, which is the range of the measured variable that the instrument measures with the specified accuracy.The minimum and maximum values of the measurement range are called the lower limit of measurement (LRV) and the upper limit of measurement (URV), referred to as the lower limit and upper limit, respectively.
The measuring range of the transmitter can be used to indicate the size of its measurement range, which is the algebraic difference between the upper limit value and the lower limit value of its measurement, namely: Range = upper limit of measurement - lower limit of measurement
Use the lower and upper limits to fully represent the transmitter's measurement range and to determine its range.If the lower limit of a temperature transmitter is -20°C and the upper limit is 180°C, its measurement range can be expressed as -20 to 180°C, and the range is 200°C.It can be seen that if the measuring range of the transmitter is given, the upper and lower limits and the measuring range can be known.
Another way of expressing the measuring range of the transmitter is to give the zero point (that is, the lower limit of measurement) and the span of the transmitter.As can be seen from the previous analysis, as long as the zero point and range of the transmitter are determined, its measurement range is also determined. Therefore this is a more common way of expressing the measuring range of a transmitter.
2. Zero shift and span adjustment
In actual use, due to changes in measurement requirements or measurement conditions, it is necessary to change the zero point or range of the transmitter, and for this purpose, the transmitter can be shifted to zero and the range can be adjusted.The purpose of range adjustment is to make the upper limit of the output signal of the transmitter correspond to the upper limit of the measurement range. Figure 2.1 shows the input and output characteristics of the transmitter before and after range adjustment.
It can be seen from the figure that the range adjustment is equivalent to changing the slope of the input and output characteristics of the transmitter, and the adjustment from characteristic 1 to characteristic 2 is the adjustment of range increase. Conversely, the adjustment from characteristic 2 to characteristic 1 is a range reduction adjustment.