Design of three-way rotary transformer/digital conversion module interface circuit

0 Introduction

The rotary transformer/digital converter is an important component for angular displacement measurement and control. It converts the angle measurement analog quantity into a digital signal and is widely used in military equipment such as aircraft attitude control and detection, missile control, radar antenna monitoring, and fire control systems. With the rapid development of integrated circuits, many products of this type of converter have been launched in the form of solid-state circuit packaging. In China, this type of digital converter module ranges from 12 bits to 22 bits, and the conversion accuracy can basically meet the application requirements. However, due to the limitation of the internal response speed of the digital converter, the converter can only track the shaft angle changes within a certain speed range. In a digital conversion system that requires a high switching speed of multiple signals, when a digital converter module is used to control the digital output of multiple signals, it will inevitably lag behind the change of the shaft angle. In order to accurately obtain the angle signal, it is necessary to increase the time period of multiple angle measurements. For this purpose, a three-way rotary transformer/digital conversion module interface circuit based on the ISA bus is introduced. The circuit has been successfully applied to the measurement of three attitude angles of a certain platform inertial navigation, with fast angle measurement speed and high accuracy.

1 Working Principle of Resolver/Digital Conversion Module

The resolver/digital conversion module is an important component of the circuit. According to the requirements, the 19-bit resolver/digital conversion module of model 19XSZ2413-S32 produced by the 716th Institute of China Shipbuilding Industry Corporation is used, and its angle measurement accuracy can reach 10". The resolver/digital conversion module produced according to the basic principle of the resolver/digital conversion module includes a coarse channel resolver to digital converter, a fine channel resolver to digital converter, a dual-speed processor and a three-state latch. The coarse channel resolver to digital converter converts into a 12-bit digital angle, and the fine channel resolver to digital converter converts into a 14-bit digital angle. The two digital angles are then processed by a dual-speed processor for hardware real-time error correction and coarse and fine combination, and then a 19-bit parallel digital angle is output to the latch. The internal principle block diagram of the module is shown in Figure 1.

2 Hardware Design and Analysis

The entire interface circuit is mainly composed of three parts: decoding circuit, resolver/digital conversion module control circuit and pulse width control circuit. The principle block diagram of the interface circuit is shown in Figure 2.

2.1 Decoding circuit

The decoding circuit is mainly composed of the decoding chip SN74HC154, which is used to generate the port address of the interface circuit. When the address lines SA15~SA10, SA4 and SA0 of the ISA bus are logic "0", SA9~SA7 and SA5 are logic "1", and SA1, SA2, SA3, SA6 correspond to the input terminals A, B, C, D of SN74HCl54 respectively, the interface circuit is selected. It is known that the address range of the interface circuit is: 0x03AO~Ox03AE and 0x03EO~0x03EA, among which 0x03EO~Ox03EA are the low 16-bit and high 3-bit digital signals for reading pitch, roll and heading respectively, 0x03A0 and Ox03A8 are the three-way simultaneous release and prohibition INH signals respectively, Ox03A2~0x03A6 are the INH signals for releasing pitch, roll and heading respectively, and 0x03AA~Ox03E are the INH signals for prohibiting pitch, roll and heading respectively.

2.2 Resolver/digital conversion module control circuit

The three-way rotary transformer/digital conversion module control circuit is the core of the entire interface circuit, which consists of three rotary transformer/digital conversion modules and their peripheral control circuits. The two important signals "INH" and "CB" in the rotary transformer/digital conversion module control the conversion of the input analog signal and the latch of the output 19-bit digital signal respectively. INH is the input terminal of the inhibit signal, which has been internally connected to +5 V with a pull-up resistor. When INH is logic "0", that is, the INH signal is inhibited, the data in the latch is stable after a delay of 600 ns, and the data can be read; when INH is logic "1", that is, the INH signal is released, the data in the latch is updated, and data reading is prohibited at this time. CB is the detection signal for the end of data conversion. When CB is high, it means that the converter is in the tracking conversion state, and the data output is unstable at this time; when CB is low, it means that the conversion has ended in the converter, and the data output is stable and valid at this time, and it can be read. The principle block diagram of one of the rotary transformer/digital conversion module control circuits is shown in Figure 3.

When the industrial computer is powered on, the "RES" (RESET DRV) outputs a negative pulse. At this time, the Q output of the SN54HC74 is high. This signal is used to control the INH of the resolver/digital conversion module. At this time, the coarse and fine channel sine and cosine analog signals of the three attitude angles of pitch, roll and heading output by the internal resolver of the platform inertial navigation enter the 19XSZ2413-S32 resolver/digital conversion module, which is the initial state of the circuit. After that, the resolver/digital conversion module controls the output of the address decoding through programming to realize the simultaneous operation of three modules or the operation of a single module. Among them, the control of the CB signals of the three rotary transformers/digital conversion modules adopts the query method. CB is used to control the enable terminal LE of the latches U1, U2 and U3 (SN74HC373). Since the output is a 19-bit digital quantity, three SN74HC373 are used. When the data conversion is completed, CB automatically becomes low, thereby enabling LE. When the CPU reads the data, the latch OE is enabled, and the 19-bit conversion data is simultaneously entered into the three latches waiting for the CPU to read.

2.3 Pulse Width Control Circuit

The pulse width control circuit is mainly used to control the I/O CS16 on the ISA interface board. When the I/O CS16 signal is valid, it notifies the system board that the current data transmission is a 16-bit I/O cycle with a waiting state. In the circuit debugging, by adjusting the size of R1 and C11, the time of the I/O CS16 low pulse can be controlled, so that the low 16-bit data can be read correctly and stably through the ISA bus. Now the circuit uses three rotary transformers/digital conversion modules to control the conversion output of three angle measurement signals respectively. When INH is logic "O", after a delay of 600 ns, CB is "O", and the CPU is

4 Experimental Results

Using the signal generated by the existing digital/rotary transformer board in the laboratory as input, the angle test results are shown in Table 1. The experimental results show that the angle measurement accuracy can reach 10", which meets the accuracy requirements.

5 Conclusion

The interface circuit has been applied to the measurement of three attitude angles of a certain platform inertial navigation and works normally, proving that the circuit design is reasonable. The angle measurement accuracy in the circuit reaches 10", which can meet the accuracy requirements. More importantly, it shortens the angle measurement cycle of the three attitude angles of the platform inertial navigation system, achieving the purpose of application.