4 to 20 mA transmission load capacity of 255

In order to reduce the number of steps, the signal is transmitted by 2 wires as much as possible, 4 mA is to transmit a sensor working current, 4-20 mA minus 4 mA to get 1-6 mA is the analog signal to be transmitted, and at the same time, in order to facilitate the conversion of the current signal into a voltage signal, and twisted pair.

impedance of transmission characteristics.

50 ohms, then 20 mA x 50 ohms is 1V, this voltage is relatively easy to achieve AD conversion.

Therefore, the upper limit is determined to be 20 milliamps, and in many cases the load resistance is selected as 250 ohms or 500 ohms.

You can press and hold the volume down button and the power button at the same time in the shutdown state,About ten seconds or so will appear in the flash interface,Select the option not to clear the data,After that, it will boot into the main interface,At this time, the interface is no pattern lock,If it is useful, please choose me Oh, you can press and hold the volume down button and the power button at the same time in the shutdown state,The flash interface will appear in about ten seconds,Select the option not to clear the data,After that, it will boot into the main interface,At this time, the interface is no pattern lock, If it's useful, please choose me, you can press and hold the volume down button and the power on button at the same time in the shutdown state,About ten seconds or so, the flashing interface will appear,Select the option not to clear the data,After that, it will boot into the main interface,At this time, the interface is no pattern lock,If it's useful, please choose me。

4-20 mA is the voltage voltage is 2V, the output standard of the output type sensor, the voltage generated by different matching resistors at the terminal is different.

The following are also included:

If connected to 100, there is a static current of 4mA, if the line is broken, the current is zero, easy to identify.

There are many factors to consider when formulating analog signal transmission for industrial automation control, and there are roughly 0-5V, 0-10V, 4-20mA, 0-20mA these ways.

0-5V is specified to be compatible with the input voltage range of most AD converter chips.

0-10V is specified to increase immunity and to weigh the output capability of an op amp at 24V or 12V operating voltage.

For 4-20mA, it is the most commonly used standard for current loop transmission, in order to reduce the number of wiring, the signal is transmitted using 2 wires as much as possible, and 4mA current is to transmit one sensor working current.

4-20mA minus 4mA to get 0-16mA is the analog signal to be transmitted, and at the same time, in order to facilitate the conversion of the current signal into a voltage signal, the characteristic impedance of twisted pair transmission is 50 ohms, then 20mA multiplied by 50 ohms is 1V.

This voltage is relatively easy to achieve AD conversion, so it is determined that the upper limit is 20mA, and in many cases, the load resistance is selected as 250 ohms or 500 ohms, and it is easy to realize the voltage signal of 4-20mA to 1-5V or 2-10V.

0-20mA is the three-wire current loop transmission standard, adding 1 power cord to power the sensor, 4mA stealing current is not needed, so that the range is extended to 0-20, and the signal resolution is increased.

If it is a signal transmitted by the instrument, it corresponds to 0 5V, or 0 10V.

The reason for using current transmission is that it can be transmitted over long distances, because the load input resistance and the line are connected in series, so the current does not change, and the signal is not attenuated due to the resistance (internal resistance of the transmission line) generated by the long line length.

Second, the current is interfered with by the outside world, and the signal is small.

4 20mA current, if a 250 ohm resistor is inserted, the voltage signal of 1 5V can be restored.

ADC converter, microcontroller required.

Because the transmission is linear, the corresponding 20mA is the full-scale value of the power meter, and the corresponding half of the current is half the range value, which can be calculated proportionally.

It is easy to convert, it takes a long time to become standardized, and the equipment is so used, or it has to be changed.

1) RS232 is full-duplex transmit and receive can be carried out at the same time.

2) The RS485 is half-duplex, and the sending and receiving cannot be done at the same time.

The transmit and receive toggle switches need to be controlled.

3) After the master sends instructions to the slave, it needs to delay the code and then read the input buffer.

Normally, the load capacity of the transmitter is related to the power supply, load = voltage and current, for example, if you are 24V power supply, then r = 24 20 = ohms, because there are some components inside the transmitter that need to use up a small part of the voltage, so the load generally should not exceed 1k ohms, if you are 12V power supply, then the load should generally not exceed 500 ohms.

This is an international standard for signal transmission. There are two main reasons why the starting current is 4mA instead of 0. One reason is to avoid interference, and the other reason is that the two-wire system is used in 4-20ma, and the two wires are signal lines, which are also the source lines of electric gods, and 4mA is to provide static working current for the circuit.