Instrument's basic performance index Measurement range: 0.lPaO.IMPa Indication accuracy: 20% Response time: QD-3 low vacuum relay circuit block diagram shown in Figure 1. The sensor used to measure the pressure is a metal resistance vacuum gauge. Inside it, a metal wire with a diameter of the order of micrometers is used as a hot wire, and is wound into a spiral shape to increase its seismic performance, and at the same time it increases the upper limit of the measurement. The hot wire temperature works in a constant state, ie keeping the hot wire temperature constant. When the pressure changes, the heating power of the hot wire changes. By changing the power supply voltage of the bridge and maintaining the balance of the bridge, the temperature of the regulatory hot wire is kept constant, and the bridge power supply voltage value has a certain corresponding relationship with the vacuum degree. However, this relationship is non-linear, and therefore, this voltage needs to be Make nonlinear corrections. The nonlinear correction is performed in a digital form. Its purpose is to convert the voltage signal of the reaction pressure into a digital signal after the A/D converter is converted into a digital signal and carry out a non-linear correction. At the same time, the digital signal is sent to the microcontroller in the form of a BCD code. In order to step into the process. This instrument is used to store the digital signal of the reaction pressure and the displayed BCD code in the EPROM. The digital signal of the reaction pressure is used as the address of the memory. The displayed BCD code is stored as content in the EPROM. One-off digital processing completes the nonlinear correction and completes the decoding function.

Figure 1. Line structure block diagram In order to realize the intelligent and automatic relay, the MCU plays a key role. This instrument adopts 89C2051 single-chip computer of ATMEL Company, it realizes the following six functions: When the digital signal that reflects the pressure is sent to EPROM, the data output end of EPROM has the data to export, the one-chip computer reads in the pressure data to be displayed from among them, Stored in the register of the one-chip computer, send to the display.

The one-chip computer takes the pressure data stored in the internal register and sends it to the display driver integrated circuit through the SPI bus. The driver IC directly drives the four-bit light-emitting diode to display the pressure value in real time.

The upper and lower limits are set on the instrument panel. There are two buttons, one is a digital adjustment key that can adjust the value, and the other is a function key that can change the digits. The single-chip microcomputer enters the parameter setting state by responding to the button request and presses the two buttons respectively to complete the numerical setting of the upper and lower limits. Stop pressing the two keys, three seconds later, the instrument automatically enters the monitoring and control state.

The adjustment range of the lower limit cannot exceed the upper limit value, and the minimum difference between the upper and lower limits is 0.1 (in the same order of magnitude).

When the instrument automatically enters the measurement and control state, the set upper and lower limit values ​​are automatically stored in the EEPROM to be called by the MCU.

After the microcontroller reads in the pressure data, it compares it with the upper and lower limit values ​​that have been set. If the size is greater than the upper limit, the over-limit output will be generated; if it is lower than the lower limit, no over-limit alarm output will be generated; The original state remains unchanged. The alarm output is sent by the microcontroller output control signal to the relay, relay action, at the same time, the alarm indicator light.

The instrument has an interface with the PCA to communicate pressure data to the PC in response to PC commands. Because the output level of the one-chip computer is TTL level, and the PC is equipped with RS-232C standard serial interface, the electrical specification of the two is inconsistent, so to finish the data communication of PC and one-chip computer, must carry on the level to change. The instrument uses ICL232 application-specific integrated circuit to achieve level conversion. There is asynchronous communication between them. After receiving the interrupt request from the PC, the instrument transfers to the program for sending data. The baud rate is 2400b/s, and the data format is: 8 data bits, 1 start bit. , 1 stop bit. The PC uses a query to send and receive data.

four. The characteristics of the instrument QD-3 low vacuum relay adopts intelligent design, as a vacuum system monitoring instrument, has many characteristics, such as most of the occasions have a strong environmental interference and electrical interference, therefore, the instrument must have Strong anti-interference ability, for this instrument to take the following measures: In the preamplifier circuit, the use of stable operational amplifiers, increase the area of ​​the ground to increase the electromagnetic shielding ability.

In the microcontroller and digital circuits, hardware dog circuits are used to prevent the program from entering a dead state.

Digital filtering techniques are used on the software to prevent sudden data changes caused by strong interference.

The use of integrated voltage regulator circuit to improve the overall power supply stability.

The use of an integrated aluminum alloy case enhances the overall machine's anti-jamming capability. The integrated circuit design is used in the instrument and the compact structure design minimizes the size of the instrument and uses a panel-mounted case for use. Centralized control system. Especially when there are multiple low vacuum relays to be installed in a control cabinet, it will not occupy too much area on the control panel.

In the comparison of the upper and lower limits of the pressure value, the instrument uses a digital comparison. Therefore, the comparison accuracy is high, and the minimum difference between the upper and lower limits is also small, which is only 0.1 in the same order of magnitude, which is unmatched by analog comparator circuits. of.

The instrument can react quickly to changes in pressure and can output data in less than 50 milliseconds. This can effectively achieve rapid protection.

Since the instruments are all using single-chip microcomputer, the output data is very convenient. It not only can carry on the wired communication with the PC or other instruments, but also, allocates the appropriate connection, but also carries on the wireless communication. This greatly improves the flexibility and practicality of the instrument. It is possible to realize intelligent control, automation and networking.

three. Application QD-3 low vacuum relay can not only measure the pressure, but also can automatically control the pressure. Its application range is very wide. For example: Under many vacuum obtaining situations, the front pump (such as oil mechanical pump) does not need continuous Work, when the pressure reaches the required lower limit, stop the pump work, when the pressure value rises to the upper limit, turn on the pump. The upper and lower limit control functions of this instrument are meeting such control requirements.

Some high-vacuum systems use two-stage pumps to pump air. When the pump is pumped to a certain pressure, the rear-stage pump is turned on. At this time, as long as the upper limit of the instrument is set, and the lower limit value is set near the upper limit, the instrument can be used as a single limit. For example, in the oil diffusion pump system, when the mechanical pump is pumped to a certain pressure, the oil diffusion pump electric furnace is automatically turned on.

In the vacuum system, in order to prevent accidents and cause damage to the system or the device, it is often necessary to protect the instrument's rapid response (less than 50 milliseconds) performance, to meet this requirement. If the ionization vacuum gauge prevents the exposure of the atmosphere and burns the filament, the use of this instrument can quickly turn off the power supply system of the filament to protect the filament from damage.

In the production of electric light sources, quantitative gas inflation is required. Using this instrument, additional auxiliary devices (such as gas tanks, electromagnetic vacuum valves, etc.) are used to realize the inflation automation.

In addition, the application of QD-3 low vacuum relays in high-energy physics, space simulation, chemical engineering, medical treatment, and electronic equipment is practical and feasible, and it is necessary to achieve automation and intelligent control.

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