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What are the functions and uses of the calculator?

What is the function and use of the calculator?
(1) Differences in the ability to handle flow signals There are many domestic manufacturers of flow display instruments. There are also many varieties of foreign similar products sold in the Chinese market. Some manufacturers can supply products with only the integrated calculation function, such as Yokogawa. The company's STLD-101*E flow totalizer, Foxboro's 75RTA flow totalizer, etc., some manufacturers only have flow display instruments with temperature and pressure input channels, but do not use their temperature, pressure input channel In the case of the case, it can also be used for simple flow indication integration. Some manufacturers make instruments that process analog flow input signals and pulse flow input signals into two products. Some manufacturers use 8 to 1 analog switch to make a meter have the ability to process 8 channels of flow input signals.

(2) Difference in the total number of display digits The flow display device displays LEDs and LCDs commonly used in digital display devices. The number of digits displayed on the LCD is generally up to 8 digits in decimal, and the LED display is generally 6 to 8 digits. In the total amount, some users want the number of digits to be longer, so some manufacturers have designed a segment display method, that is, a total of 12 digits (or 16 digits) of total decimal display, which is often displayed on the panel. Bit (or 8 bit), press the special defined reading button to display its high 6 bits (or 8 bits), and give the high segment flag, so that it will not accumulate zero in several years, thus making up the bit. A defect that is not long.

(3) Difference in accuracy level The accuracy of the foreign production flow display instrument is generally set higher, while the domestic flow display instrument is mostly in the 0.5 and 0.2 levels. This is mainly related to the accuracy of the selected AlD converter. The AlD converter used in the meter is generally double-integrated type, and the conversion speed is slow, but the stability is good, the code hopping is small, and the anti-interference ability is strong. The high-precision AlD converter has high resolution and high accuracy, but the price is relatively expensive. The low-precision 8-bit AlD converter is also used in 0.5-level precision products due to its low price.
The domestic flow meter for measuring the pulse flow input signal, the total measurement accuracy is generally set higher, but the instantaneous flow accuracy is quite different, the accuracy is determined to be 0.1% R, and some are fixed. It is ±0.5% R or even ±1%R. The analysis is mainly because the instantaneous flow rate is different. The former is a computer method, that is, the average frequency of the input signal is measured by the single chip when the input signal frequency is high. At lower frequencies, the pulse averaging period is measured by the microcontroller and then the instantaneous flow is calculated along with the flow coefficient. The latter is based on the RC integration technique. The input pulse is sent to the RC integration circuit to obtain a voltage signal proportional to the frequency. After smoothing, it is sent to the AlD converter to obtain the digital quantity, and then displayed. Due to the many conversion links and the defects of the f/V conversion method itself, measurement accuracy is difficult to improve.

(4) Differences in communication standards Domestic communication display instrument communication ports are generally RS-232 or RS-485 field bus standards, but some foreign early products have other standards such as RS-422, and the recently launched products have basically been unified. RS-232 or RS-485 standard. Some can also provide interfaces such as FF fieldbus.

(5) Differences in indicators such as electromagnetic compatibility Some foreign manufacturers have also done a lot of work on environmental compatibility such as electromagnetic compatibility of products. For example, FOXBORO's 75 series flow display instrument has a radio frequency electromagnetic field radiation immunity index of 3V/m, 27 to 1000MHz, and its dusttight watertightness index is set to IP65. In these two tests, the domestically produced flow meter was basically not carried out.

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