Device and method for detecting connectivity of digital input signal line

Abstract

Provided are a device and method for detecting the connectivity of a digital input signal line of a PLC. The digital input signal line is serially connected with sensors which are powered by a DC voltage. The device includes capacitors which are connected in parallel with dry contacts of the sensors; and a three-end switch. A public end (K) and a first contact end (K1) of the three-end switch are serially connected to the digital input signal line. The first contact end of the three-end switch is connected to an input public end of the digital input signal line. A second contact end (K2) of the three-end switch is connected to the DC voltage. When connection and disconnection of the public end (K) to the first and second contact ends (K1, K2) of the three-end switch are controlled through an internal part of the PLC, the device judges whether open circuits exist in the digital input signal line of the PLC according to whether current pulses are detected by the PLC in digital input channels.

Description

technical field [0001] The invention relates to a device and a method for detecting the connectivity of digital input signal lines in the field of industrial control. Specifically, it relates to a device and a method for detecting the continuity of signal connection lines connecting dry contact output signals of various sensors to digital input terminals of a programmable controller (PLC). Background technique [0002] In the field of industrial control, various sensors are usually used to obtain the variation of the controlled point, and the detected variation is transmitted to the PLC through the signal line for processing. Generally, the sensor outputs a signal representing the above-mentioned variation through its dry contact. [0003] However, when the PLC input terminal is a digital input terminal and the sensor outputs a sensing signal via its dry contact, if the signal line connecting the sensor output terminal and the digital input channel of the PLC input terminal...

AI Technical Summary

Problems solved by technology

[0009] 1) For each digital input channel of the PLC controller, a test or comparison circuit needs to be designed, which is very complicated and increases the cost;

[0010] 2) It is not easy to choose the resistance value of the resistors connected in parallel or in series in each digital input channel, because for different types of digital input channels of PLC controllers, different field modules, and different manufacturers, the selected resistors resistance values ​​vary

[0011] 3) There is always a test current in the test circuit, which also increases the power consumption of the product

[0012] 4) For some old PLC products or systems, it is difficult to detect the connectivity of signal lines

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