How to use the input module plc 's multi- segment level setting , display, alarm and automatic level control

In many production areas , it is often necessary to tanks , storage tanks, pools and other containers of liquid level monitoring to the usual traditional relay -contact control , multi- use hard-wired electrical  plc manufacturer appliances , poor reliability, high degree of automation , has there are many enterprises to adopt advanced controller to transform the traditional exposure control , greatly improving the reliability and automation level of the control system , providing a more reliable production guarantee. This paper describes a programmable controller (PLC) A method for monitoring liquid level , its simple circuit structure and low investment ( Available renovation of existing facilities ) , not only a high degree of automation control systems , but also has online modify the function , flexibility, suitable for Nanda cpu module plc  multi- level monitoring applications.
1 . Control requirements
The control system can be based on the needs of production is divided into multi- level set , and segment display , when the minimum level to start automatically when you add liquid feed pumps , liquid level reaches the set value audible alarm and stop the pump ; the operator can turn plain by the OK button to lift the alarm sound , flashing lights ; system with manual / automatic control modes , and a test function.
2 . PLC Selection
In this case , select the PLC PLC should consider the cost performance , high reliability, choice , quite , load capacity suitable , affordable PLC. This article introduces the four level control object , for example, according to analysis and comparison of a variety of plc input output modules  factors and control system input and output points requirements.
3 . System hardware configuration
To achieve the level of manual / automatic control, you need to enter the mouth 12:00 , 8:00 outlet , use C20P 20点PLC I / O unit , optically isolated input and output isolation relays , load capacity ; liquid level detection using Reed tube sensor , manual / automatic conversion , run / test conversion and level settings using double- knob manually start the pump , the pump stops and confirmation test using normally-open button ; selection of electronic sound alarm output and 24V DC lights, relays . See Figure a hardware configuration diagram