This paper presents a signal conversion circuit of pump cabin based on lc2294 processor, which realizes the acquisition and processing of three channels of 4-20 mA current signal, and converts 4-20 mA current signal into 0-1.6 MPa pressure signal. When the pressure signal exceeds the set threshold, the pressure overrun light alarm is given, and the conversion error is less than 0.01 MPa. At the same time, the pressure data passes through 10 / 100 Mbit · s-1 The self-adaptive dual redundancy Ethernet is transmitted to the upper computer, and the data transmission frequency is more than or equal to 5 times / s.
Design of signal conversion circuit
LPC2294 is used as the main controller of the signal conversion circuit. Two 10 / 100 Mbit · S-1 adaptive network card interfaces are expanded, and μ C / OS-II real-time operating system is used as the control platform. The TCP / IP protocol stack is cut and implemented, and the data receiving conversion of pressure sensor and data sending through Ethernet are completed through software design. The hardware circuit design includes six parts: main control circuit, pressure signal receiving circuit, analog-to-digital conversion circuit, storage circuit, Ethernet interface circuit and auxiliary circuit.
Analog to digital conversion circuit
In this design, the standard 5 V power supply is used to supply power to ad7888, and the analog pressure signals which have been converted into voltage form are sent to analog signal pins 1 to 3 respectively. The level of LPC2294 is 3.3 V, while that of ad7888 is 5 v. Therefore, LPC2294 needs level conversion for the control signal of ad7888, which can control ad7888 stably. In the design, 74lvc245 is used for level conversion. The chip selection signal, clock signal and data input signal from LPC2294 chip are sent to 74lvc245, which are input to ad7888 after level conversion. Because LPC2294 can withstand 5 V voltage, the output data after analog-to-digital conversion is directly sent to the p0.28 pin of LPC2294. The specific circuit is shown in Figure 2.
Figure 2 analog to digital conversion circuit
Design of Ethernet interface circuit
The Ethernet interface circuit is mainly composed of DM9000E Ethernet controller and hr601860 network card transformer. DM9000E is a low-power, highly integrated, high-speed Ethernet control chip designed by davicom company. It can be directly connected with CPU and support 10 / 100 Mbit · S-1 Ethernet connection. The interface supports 8-bit, 16 bit and 32-bit processors. The system is designed as two network ports, one is main network port, the other is redundant network port. LPC2294 and DM9000E are connected by 16 bit bus and set in 100 MHz full duplex mode. By controlling the CS2 and CS3 pins of LPC2294, the chip selection signal is output to select the two network ports. In the circuit design, CS2 and CS3 are connected with pins A2 and A1 of 74hc245, and pins 74hc245b1 and B2 are connected with redundant NIC chip and ane pin of main NIC chip respectively. Then connect the two CMD pins of DM9000E chip with A2 of LPC2294. The data port address and index port address of the main network card chip and the redundant network card chip can be configured as 0x83800000, 0x8380004 and 0x83400000, 0x83400004 respectively. The physical layer transmit and receive ports TXO +, TXO -, RXi +, RXi – of DM9000E are respectively connected with tpout +, tpout -, tpin +, tpin – of hr601680. As shown in Figure 3.
Under the premise of increasing concern for ship safety, this paper proposes a design of signal conversion circuit for ship pump cabin, which is convenient for real-time monitoring of the working state of ship pump, so as to achieve early warning of abnormal state. With ARM7 series LPC2294 as the core controller and other chips, the design realizes the communication function of transmitting the pressure data from the pressure sensor to the Ethernet through the network card. The reliability of the signal conversion system is verified by experiments. In addition, for the misjudgment of automatic acquisition technology, the next research direction can effectively fuse the collected data to improve the accuracy of data and reduce the occurrence of misjudgment.