Abstract: This paper introduces the design of a rudder potentiometer tester based on an embedded PC104 microcontroller, suitable for C38-16 microcontrollers. By interfacing the tester with the rudder potentiometer, a precision voltage source and a precision constant current source are controlled by a relay array to test the rudder potentiometer and determine its qualification. The working principle of the rudder potentiometer is analyzed, and the functions achieved by the tester are explained. Experiments and analysis show that the tester can determine the qualification of the rudder potentiometer with a measurement accuracy of 0.3% and an aesthetically pleasing design, thus demonstrating the superiority of this system.
Keywords: Embedded PC104; Steerable potentiometer; Tester; Relay array
Abstract : This article introduced the design of a helm potentiometer instrument based on embedded PC104, this measure instrument is appropriate to C38-16. Collecting helm potentiometer to measure instrument, using of relay array to control precision power supply to test helm potentiometer.and then deciding helm potentiometer is up to standard or not.Analyzed principle of helm potentiometer and expounded this instrument's function of consummating.The test and analysis show that the measure instrument can determine whether helm potentiometer is qualified or not, the accuracy of this instrument measurement is less than or equal to three in a thousand , the sculpt look beautiful, and then advantage of the system is proved.
Key words: embedded PC104; helm potentiometer; measure instrument; relay array
In recent years, PC104 technology has developed rapidly. It features an IDE interface for connecting external hard drives and optical drives, as well as parallel and serial interfaces, and can be expanded with a network interface. In embedded applications, compared to industrial control computers, PC104 allows for more portable and smaller instruments. This article introduces the development of a PC104-based potentiometer testing instrument. A potentiometer is a specialized instrument with high accuracy requirements, making testing cumbersome. Before use, a potentiometer may have some problems due to various reasons, and without testing, it may not function properly. Therefore, we developed a potentiometer testing system to ensure its normal operation.
1. Working principle of the rudder potentiometer
The rudder potentiometer is an important instrument in the missile control system. Its function is to provide feedback on the deflection of the missile's gas-fuel rudder, sending the information to the computer for processing. This information is used for missile guidance and stabilization, and it is a crucial component of the guidance and stabilization systems during the missile's active phase of flight. Its working principle is shown in Figure 1. In Figure 1, points 12 and 13 are electrically connected to points 18 and 22, while points 10 and 11 are mechanically connected to the sliding contact. When the gas-fuel rudder deflects, it causes the rudder potentiometer to deflect, and the sliding contact reaches the electrical limit point. The limit signal input and output contacts then make contact, and output 2 of the rudder potentiometer becomes the limit signal. Simultaneously, outputs 1 and 2 are combined into a single signal, which serves as a feedback signal and is sent to the onboard computer to limit the deflection of the gas-fuel rudder.
2. Overview of the Functions of the Steerable Potentiometer Tester
By connecting the tester to the rudder potentiometer and using a relay array to control a precision voltage source and a precision constant current source to test the rudder potentiometer, the tester determines whether the rudder potentiometer is a qualified product. The test results are displayed visually on the screen and can be stored and printed. The tester's functions include: rudder potentiometer self-test, contact reliability detection, resistance performance testing, operating angle detection, and voltage performance testing.
Figure 1. Circuit diagram of the rudder potentiometer
3. Hardware Design of the Test Instrument
3.1 Hardware Composition of the Tester
The hardware of the rudder potentiometer tester consists of a PC104 and its peripheral circuits, a measurement circuit, and a control circuit. The hardware circuit structure diagram is shown in Figure 2.
Figure 2 Hardware circuit structure diagram of the potentiometer tester
Because the output of the rudder potentiometer is significantly affected by power supply accuracy, especially ripple voltage, the power supply applied during testing should be relatively stable; therefore, a regulated power supply is used. The A/D converter has 9 bits, which can reduce the measurement error to 0.3%, meeting the design requirements. The measurement circuit consists of analog switches, a preamplifier circuit, and an A/D converter, realizing multi-point measurement of the rudder potentiometer's resistance and voltage, and converting the measured physical quantities into digital quantities for input to the computer. The control circuit consists of I/O circuits and a relay switch array, providing the voltage and current required for rudder potentiometer testing. The control channel automatically switches and loads according to the program. The power supply circuit consists of a regulated power supply and a constant current source, satisfying the relay switch array drive and providing a high-precision source for rudder potentiometer measurement. The stepper motor control feedback circuit completes the rotation drive and positioning control of the rotary table. For the industrial control computer, an embedded PC104 industrial control computer was chosen for reliability considerations, using the industrial computer as the core to automate the product testing process. The touch screen completes the setting of status and parameters, and simultaneously displays the test results on the touch screen to judge the correctness of the measurement data. The communication interface includes an external keyboard and mouse, and a USB port is used for data storage, export, and connection to a printer to output test reports.
3.2 Measurement Method
The measurement method is as follows:
(1) Potentiometer tester self-test
If a self-test is required, connect the test shorting connector to the X38 interface of the tester. During the self-test, the shorting connector method is used. The potentiometer tester automatically measures the resistance values of the connections, relay switches, and circuits of each channel, and stores and saves this data. When the tester performs a rudder potentiometer measurement, it automatically subtracts this data to ensure the accuracy of the measured resistance.
(2) Potentiometer contact reliability test
When the control circuit connects pins 3 and 16 of the left and right rudder potentiometers together and automatically applies a DC+5V voltage to the two sliding contacts pins 5 and 18, the measurement circuit reads the test process data at a 1K sampling frequency. Alternatively, an external oscilloscope can be connected to observe the waveform to complete the potentiometer contact reliability test.
(3) Potentiometer resistance performance testing
The control circuit automatically connects the current source to pins 3 and 7 of the potentiometer, the COM terminal to pin 1, and the COM terminal of the measuring circuit to pin 1. It automatically reads the voltage data from pins 3 and 1 (or pins 7 and 1), inputs the measured data into the computer, and calculates the total resistance and half resistance values of the potentiometer. The same method can be used to detect the total resistance and half resistance values of another potentiometer.
(4) Potentiometer working angle detection
The control circuit can automatically output indications and controls based on the electrical closed contacts 10 and 12 of the rudder potentiometer.
(5) Potentiometer voltage performance testing
The control circuit automatically connects the voltage source (DC+15) to pin 1 of the potentiometer, the voltage source (DC-15) to pin 3 of the potentiometer, the COM terminal to pin 7, and the COM terminal of the measuring circuit to pin 7. The user manually inputs the measurement angle range, and the tester automatically reads the voltage data from pin 5. The data is input into the computer to calculate the zero-point coincidence and insensitive area of the potentiometer. The same method can be used to test another potentiometer.
(6) Automatic measurement
The potentiometer testing process is controlled by the PC104 embedded industrial computer. All required test items are set manually, and the tester automatically completes the tests in sequence. When manual input of parameters or data is required, the tester will display prompts to guide the user.
4. Tester Software Design
The rudder potentiometer tester is an automatic measuring device. The software is written in Visual C++ 6.0 and Windows XP, and the human-machine interface is very user-friendly, making it easy for operators to use.
4.1 Tester self-test
The operating interface of the rudder potentiometer tester software is shown in Figure 3. Click "Tester Self-Test" to enter the rudder potentiometer self-test subroutine and enter the self-test interface, as shown in Figure 4. Click "Start Self-Test" to start the self-test. The items checked are shown in Figure 4, and the results will be displayed in the corresponding columns in Figure 4. After the device self-test is complete, remove the short-circuit connector and connect the rudder potentiometer to the tester to prepare for the rudder potentiometer test.
Figure 3 Main interface of the rudder potentiometer tester
Figure 4 Self-test interface of the rudder potentiometer tester
4.2 Rudder Potentiometer Test
Returning to the self-test unit of the tester, you will be returned to the main interface of the test software, as shown in Figure 3. Click to enter the unit test. The program calls the unit test subroutine and enters the unit test interface, as shown in Figure 5. Click "Start Test" to begin the unit test of the potentiometer. The first step is the resistance test, as shown in Figure 6. Click "Start Measurement," and the system will begin testing the resistance performance of the potentiometer. After the test is completed, the measurement results will be displayed in the corresponding column.
Figure 5 Unit test interface
Figure 6 Resistance test interface
Resistance is measured by applying a 5 mA constant current source to the object under test, then sampling the voltage at the positive terminal of the applied current, and calculating the resistance based on the voltage and current of the object under test. After the resistance test is completed, click "Confirm," and a prompt will appear asking "Proceed to the next test item?" Click "Yes" to proceed to the electrical closure angle and mechanical limit angle tests. The operating angle test can be determined by detecting the limiting signal. If there is no limiting signal, it indicates that the rudder potentiometer has not reached the electrical limit point. If it has reached the electrical limit point, the limiting signal can be detected, and the angle corresponding to the electrical limit point is the operating angle. The mechanical limit angle is the rotation angle corresponding to the mechanical limit point. It can be determined by touch. When the turntable cannot be moved, move the turntable in the opposite direction; the rotation angle at the turning point is the limit angle, which is stored in the computer. The same method can be used to complete the insensitivity zone test, zero-point coincidence test, and uniformity test. During the test, it was found that even in the linear part of the input rotation angle and output voltage of the rudder potentiometer, the relationship is not strictly linear, but rather resembles a hysteresis loop. Therefore, during testing, the turntable can be rotated in both left-to-zero and right-to-zero directions, and the output of the rudder potentiometer can be sampled at the zero point to measure the zero-point coincidence (zero-position voltage). After the measurement is completed, click "Confirm" to end this unit test. Clicking "Exit Test" in the unit test will bring up the main interface of the test software again. Clicking "Single Step Test" on the main interface will enter the single-step performance test interface. Here, you can select the performance to be tested, and the specific method is the same as the unit test. Similarly, you can set the parameters of the tester and the data management information of the tester.
5. Conclusion
The rudder potentiometer tester designed in this paper can accurately determine whether the rudder potentiometer is qualified, achieving a test accuracy of 0.3%, reducing measurement time, and is a significant improvement over previous test systems. It also reduces the complexity of operation and has an aesthetically pleasing user interface, thus possessing good application value.
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