Pls 4 voltage of the 20mA current signal

No. The current signal of 4-20mA of the control frequency is not internal, and it must be given externally to the frequency output of the inverter. For example:

Thermometer with PID adjustment, output 4-20mA, flow meter, etc. If you don't turn on the inverter to see the frequency control**, you can only know if you adjust the parameters to see it, or power on the test run.

The output of the frequency sensor is 4-20mA is a current flow, (of course, the current must have a voltage, his no-load voltage I measured, when the flat rate is 50Hz, the voltage is about 8V, but this voltage is changed with the load, it cannot be loaded, the corresponding current flow is indeed constant), because the current is very small, so it is not possible to use passive instruments,

The current signal itself has no voltage, and a resistor connected in series can produce a corresponding voltage.

An active signal is not required.

Passive signals can be used. Not visible from the control panel. Generally, there is a DIP switch sign near the control terminal under the control panel, and the corresponding toggle switch of AI1 is 0-10V in the direction of "AI1"; Otherwise, it is 0-20 mA or 4-20 mA (depending on the parameter).

The signal type of the external wiring should be the same as that of the DIP switch.

It is not possible to see or define the type of input from the control parameters of the dashboard alone.

Added: The parameter 1103 setpoint determines which physical channel a given speed comes from. When the value is equal to 0, the given amount (the amount of frequency modulation that works) comes from the keyboard setting; When equal to 1, the given amount is from AI1; When equal to 2, the given amount is from AI2.

Manuals are available online for free**. Various brands of inverters, hardware (wiring) and software (parameter settings) are similar, the difference is only that the large capacity to be connected to the external filter inductor, the simplified version (mini) lacks some input and output signals.

I have n ways to do this.

The most accurate way is to connect a current sampling resistor, 1 ohm is enough, and then collect the voltage at both ends of the resistor, then the subtractor, subtract the voltage generated by 4mA, and then pass through the co-directional (reverse) amplifier, you need to choose the appropriate amplification, if you use a 1 ohm sampling resistor, you need to amplify the signal 250 times, and then output.

Another method is to connect the output of the current to the base of the triode through the current amplification of the triode, and then add a current sampling resistor to the radiation stage of the triode, you can directly use the voltage output on this resistor or after appropriate amplification and then output.

Another way is to use a current transformer, which is actually a transformer with a certain primary impedance. When the input current changes, the voltage on the primary coil is also changing from Ohm's law, and you can get the 0-5V you want by boosting the voltage of the transformer, which is a little more troublesome to make.

The above are three methods, I personally recommend you to use the first one, the circuit output accuracy is high, and it is not complicated.

In practice, it is measured in the following ways:

1. According to the conventional circuit current measurement method, disconnect the signal loop and connect the ammeter in series in the signal loop for measurement; (Figure 1).

2. Measure from the output measurement terminal or jack of the signal generation instrument. Note that an ammeter with small internal resistance must be used at this time, otherwise the measurement result will be affected; (Fig. 2-Fig. 3).

Using the voltage current conversion circuit AD694, a 0-10V voltage signal can be converted into a 4-20mA current signal.

The AD694 is a monolithic current transmitter that accepts a high level signal input to drive a standard 4-20 mA current loop to control valves, actuators, and other devices commonly used in process control. The input signal is buffered by an input amplifier, which can be used to adjust the input signal or buffer the output of a current-mode DAC.

Pre-calibrated 0V to 2V or 0V to 10V input ranges can be selected with simple pin bonding; Other ranges can be set with external resistors.

The LM324 is a follower circuit. The 4 - 20 mA current generates a voltage signal of 1 - 5V on the precision resistor, which is fed into the follower and improves the drive capability.

The signal current of 4-20mA is a standard signal transmitted by instruments and meters that is uniformly used by the International Organization for Standardization.

The starting point of 4mA is used to quickly determine whether the signal loop is open, and once the signal loop is open, the signal current will be zero. Compared with the previous use of 0mA, the starting point can quickly make a judgment, which makes it possible to quickly isolate the false detection signal and eliminate the source of the fault in the detection loop.

The current signal of 4-20mA can be converted into a signal voltage of 1-5V by the standard resistance of 250 EU, when the control loop is composed of a single instrument in the past, the signal voltage of 1-5V can be easily connected in parallel with multiple instruments, such as regulators, alarms, recorders, etc., when one of the instruments fails, it can be isolated and replaced without affecting it. Nowadays, due to the basic use of PLC or DCS as the control system, the signal of 1-5V is relatively small.

The 4-20mA current signal corresponds to the measured value only as a percentage, regardless of the size of the specific measured value. For example, the range of a pressure transmitter is 0-100kpa, then when 0kpa, it is 0 of its full scale, corresponding to 4mA, and when it is 100kpa, it is 100 of its full scale, corresponding to 20mA. The correspondence between them is:

Measured value - zero point value) (range value - zero point value)) current value - 4) (20-4))).

When the current value is known, the measured value can be calculated. Conversely, when the measured value is known, the current value can be calculated. Measurements of temperature, flow rate, level, etc., can be calculated using the same formula, regardless of the size of the measuring range.

The output trace search signal of 4-20mA means that the minimum current is 4mA and the maximum current is 20mA.

When transmitting the signal, it is necessary to take into account that there is also resistance on the wire, if the voltage is transmitted, a certain voltage drop will be generated on the wire, and the signal at the receiving end will produce a certain error!Therefore, the use of current signals as a joke is the standard transmission of the transmitter!

The state deficiencies of xtr108 are:1) Linearization circuit with sensor.

2) Digital correction. Through the SPI interface.

The XTR108 can be set directly, and the EEPROM can be directly programmed via the SPI interface.

3) The gain range of the application amplifier with programmable gain of automatic zero stabilization is multiple.

4) The resolution of the programmable current of the RTD excitation is A.

5) The correction parameters are stored in the external EEPROM.

6) Programmable over-range and under-range outputs.