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The DFP-2100 distributor is a unit in the DDZ-I electric unit combination meter. Because it can provide an isolated power supply for the transmitter located in the field, and can convert the 4-20mA DC current signal output by the transmitter into a 1~5V DC voltage signal isolated from it, the transmitter, The two-way isolation between the secondary instrument and the power supply is therefore a type of DDZ-I electric unit combination meter that is often used when controlling the production site where explosion protection is required. Since the input end of the DFP-2100 distributor can be used as a common transmission line for the power and output signals of the two-wire transmitter, it is often used when converting the physical parameters of the production site using a two-wire transmitter.
A DFP-2100 distributor can convert the output signals of two two-wire transmitters on the production site.
Due to the above advantages of the distributor, its application is very extensive. However, some technicians often fail to understand the working principle when installing, using and periodically verifying the distributor. Some wrong installation methods often occur, resulting in inaccurate output signals from the transmitter. Even when verifying the power distribution, use the signal source. If the voltage divider resistor is not properly selected, it may burn out the standard instrument for calibration.
Therefore, the correct method must be used when installing and verifying the distributor.
This paper starts with the analysis of the working principle of the distributor, and explains the technical problems that should be paid attention to during the installation, use and verification, in order to obtain the correct installation, use and verification of the distributor.
The working principle of the distributor The circuit of the distribution principle is shown as (only one of the channels is shown in the figure). The power distribution device is powered by 24V DC. The power supply from the power supply terminal is self-oscillated by a voltage regulator circuit composed of a Zener diode and a constant current source and a magnetic coupling multivibrator. The AC square wave signal of the oscillator is outputted through the secondary output of the transformer B1, and then filtered by the full-wave bridge rectifier circuit composed of BG15-BG18 and the capacitor C, and outputted by the A1 and A2 terminals of the distributor. This voltage can be used as a transmission. Power supply for the unit. Due to the two-wire transmission, the transmitter's 4-20mA DC current signal is input at the same time, coupled by the B2 transformer, converted to 1~5V DC voltage through the 250Q resistor, and output through the B1 and B2 terminals of the distributor. At the same time, B3 and B4 can output 4~20mA DC current signal for auxiliary signal. If the auxiliary signal is not used, the B3 and B4 terminals must be shorted. The distributor has two channels, each with the same function and requirements.
The correct installation and use of the distributor can be seen from the principle of the distributor. The distributor distributes the signal output from the transmitter into a current and voltage signal isolated from it, and also supplies an isolated DC power supply to the transmitter. The transmitter is equivalent to a variable resistor whose resistance is controlled by the measured parameter; when the measured parameter changes, the equivalent resistance of the transmitter also changes. When designing and installing the distributor and transmitter, the technician only needs to connect the positive and negative ends of the transmitter output signal to the positive and negative ends of the distributor input signal, and no need to add another power supply. However, when some comrades are found on site, the transmitter and the distributor are connected: a power supply, a transmitter, and a distributor. They believe that the distributor only acts as a signal isolation and conversion, and the transmitter needs to work normally, and another power supply is required, so the transmitter, the distributor, and the power supply are connected in series. If this connection is equivalent to the fact that the distributor has provided a power supply to the transmitter and a working power supply is added, the transmitter is not working properly, and the output signal converted by the transmitter is less likely to be accurate. Sometimes the transmitter may be burned out, so be sure to pay special attention to the correct connection when installing the distributor.
In addition, it can be seen from the working principle diagram of the distributor that the voltage output signal of the transmitter can be obtained from the terminals B1 and B2 of the distributor, and the current output signal can be obtained from the terminals B3 and B4, so that It is very convenient to display the meter to observe the change of the output of the transmitter. It is very easy to use these signals to control other instruments. However, if we only use the transmitter output voltage signal instead of its current signal, we must short the distributor current output terminals B3, B4, otherwise, the distributor terminals B3, B4 are quite T-open, and What is obtained from the terminals of Bl and B2 is a zero output signal. The correct connection method between the distributor and the transmitter is as shown.
The verification of the distributor is due to the fact that the Al and A2 terminals of the distributor are connected with a DC power supply as a check signal input. Therefore, when the power distribution is verified, the signal source can no longer be used to send a standard signal, and then the method of measuring the output size error is performed. . If we use this method to verify the distributor, when the shunt resistor selection is not suitable, it may burn the signal source, and the reliability and accuracy of the verification result cannot be guaranteed.
When the distributor is in calibration, the internal resistance of the transmitter should be simulated using a standard resistance box, and the input voltage should be measured from the precision resistor connected in series, and then the corresponding output voltage should be measured. The correct verification method is as shown.
When adjusting the first channel of the power distribution, the second channel needs to be connected to a 1/2W-2KQ resistor at the input end, and the power supply 24VDC can be verified by preheating for 30 minutes. The accuracy of this instrument is 0.35%. When the resistance value of the resistance box is adjusted so that the input signals on the 250Q resistor are IV, 2V, 3V, 4V, 5V, respectively, observe whether the output voltage of the distributors Bl and B2 corresponds to IV, 2V, 3V, 4V, 5V, the error should be within the accuracy range. The relevant voltage of each point is measured in turn, and the second channel is verified as described above. If the accuracy requirements are met, the instrument works normally and can be put into use.
The size of the output signal IV value generally does not have to be adjusted. The value of the output signal 5V can be adjusted by the range potentiometer (Wl, W2). The first channel range potentiometer is mounted on the right side of the fuse holder and the second channel range potentiometer is on the right side.
When verifying the output 4~20mADC signal, the external terminal 3, 4 (the second channel is 7 and 8 ends) should be disconnected, and the current meter can be connected to C3 to connect +, 4 to - the second channel 7 to +, In short, only by taking the correct method to verify and install the distributor can it play its role in modern industrial production.
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