18 - Trace

Abstract

This chapter introduces the concept of Trace, a method by which historical trend graphs can be produced. The displays can show graphically the operations of selected input/output devices, and the values stored in timers, counters and data registers. It is used in fault finding rapidly changing signals, which cannot be observed with input/output LEDs and can be used to display the logic conditions of input/output devices and the contents of timers, counters, and registers before and after the occurrence of the fault condition. The basis of Trace is that RAM memory within the PLC. The input Trace data can consist of up to 10-bit devices, that is, X, Y. M and up to 3 * 16-bit word devices, that is, timers, counters, and data registers. Each time a clock signal is applied to the Trace memory shift register, a sample of data that is the logic state of the bit devices and the contents of the word devices within the PLC is clocked into the register. The stored data in the Trace memory shift register is then uploaded into Gx-Developer and can be displayed in graphical format before and after the fault condition.