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Ocean tells you why you should choose a weighing control instrument?

In general, when we choose the weighing control instrument , the 4-20ma output is selected in many cases, especially when selecting sensors such as pressure sensors. As for why the industry uses 4-20ma output instead of other numerical outputs? I believe many people don't know why. The following is secretly told by Xiaobian, hurry to collect it -

First, because the internal resistance of the current source is infinite, only the current signal can be used to avoid interference, so that the accuracy in the series connection of the resistor is not affected, so that the function of transmitting hundreds of meters can be achieved on the ordinary twisted pair. In order to achieve the function of explosion-proof, there is generally an upper limit of 20 mA, as long as the current below 20 mA, it will not cause gas ignition on-off failure. The little friends will question why the lower limit is not set to 0 mA. The reason is that the state of the disconnection can be detected. Normally, it will not be lower than 4 mA. When there is a fault such as a broken circuit, the loop current drops. When it is 0, 2mA is generally taken as the alarm value of the disconnection.

Second, if the current type weighing control instrument is powered by an external power source, the physical quantity will be converted into a 4-20mA current output. More common is to add two current output lines based on the original two power lines, which becomes the so-called four-wire weighing control instrument.


Third, the pros should know that the 4-20mA current itself can supply power to the weighing control instrument. The weighing control instrument is equivalent to a special load in the circuit. Its special point is that the current consumption of the transmitter changes between 4 and 20 mA depending on the sensor output. The weighing display instrument can be placed in the circuit as long as it is in the circuit. Such a transmitter is only required to have two external wires, so it is called a two-wire transmitter. Because the standard lower limit of the industrial current loop is 4 mA, the transmitter will have a minimum of 4 mA in the range, so the two-wire sensor is a good choice for the load cell.

Therefore, the transmitter is generally 4-20ma signal output when selected, so that the signal is not easily interfered and safe and reliable. The two-wire 4-20ma output can save the sensor cost. These reasons make the sensor commonly used in industry. It is a two-wire 4-20ma output. Of course, many sensors now have other styles of output such as 0-5V, RS485/RS232, etc., all of which are designed to handle sensor signals very well.