The first step in on-site debugging is to test various input/output signals (IO testing). This process is sometimes not straightforward. You may find that when you press a button, the input module does not receive the signal. What could be the reason?
The reasons for the signal module not receiving signals can be broadly summarized into two categories: 1) Electrical wiring errors. 2) Drawing errors.
In the first scenario, electrical wiring errors, the only solution is to systematically troubleshoot on-site according to the drawings. This may involve a considerable amount of work, and the challenges of on-site debugging are evident.
In the second scenario, drawing errors, this may result from mistakes by the design personnel or a lack of clarity regarding module wiring. To identify this type of error, on-site debugging personnel need to be familiar with the wiring diagrams of the modules being used, allowing them to identify drawing errors and complete the debugging work promptly.
In the Siemens ET200S system, with the same baseboard module, connecting different signal modules results in different wiring methods. In other words, although the wiring terminals are on the baseboard module (TM), the definition of the wiring terminals depends on the plugged-in signal module.
Let's take the example of a 4-channel digital input (4DI) module and an 8-channel digital input (8DI) module, both connected to the same baseboard module TM-E15C26-A1, to see how the wiring differs.
First, let's take a look at the pin definition diagram for the 4-channel digital input (4DI) module:
Let's take a look at the pin definition diagram for the 8-channel digital input (8DI) module:
See that? Even though it's still TM-E15C26-A1, when connecting the 4 DI module, terminal 3 is labeled as L+ (24V). However, when plugging in the 8 DI module, terminal 3 is the input channel for DI 4.
Don't underestimate these differences. If your electrical foundation is not solid or if you are not clear about the wiring terminals of the modules, troubleshooting on-site wiring issues might take a considerable amount of time. If the project timeline is tight, it could lead to significant pressure. Wiring is a fundamental skill in debugging, so it's essential to regularly consult the manuals, build a strong foundation, and be better prepared to handle on-site issues.