When comparing PQW versus QW, users often wonder why the Edit Symbol of an Analog Output module always displays PQW. How can QW be utilized instead, and will it provide the same functionality as PQW?
As far as I recall, the "P" in PLC programming stands for peripheral, which means it writes directly to physical I/O instead of only updating the image at the end of the scan cycle. This method allows for reading and writing directly during the program scan, rather than waiting to update the peripheral image outside of the typical PLC scan.
USMAN SHAH posed a common question: What sets PQW apart from QW in the context of Analog Output modules? Upon accessing the Edit Symbol feature, users may notice that PQW is consistently displayed. This prompts the question: What purpose does QW serve? Is it feasible to substitute QW for PQW while achieving the same results? Additionally, it is worth noting that these designations are also utilized for reading and writing data to external addresses beyond the process image.
RClem explained that PLC programming often involves reading and writing to memory addresses beyond the process image. In S7-300/400 systems, Digital IO is typically included in the process image and updated in each scan, while analog IO is kept outside the process image and updated only when necessary. In contrast, in 1200/1500 systems, the entire IO area is part of the process image, simplifying the process. However, users can still utilize aat the end of an IO tag for peripheral access if needed.
I have a related inquiry regarding this topic that pertains to user programs accessing memory rather than directly interfacing with physical I/O. Data transmission between I/O image memory and physical outputs is facilitated by the PLC operating system, which may lead to discussions around the semantics of how the user program interacts with outputs. Whether utilizing PQW or QW instructions, the focus is on when data is written rather than what data is being written. Building a PLC without deep knowledge of internal implementation may make this distinction clearer. Does anyone have insights into the internal workings of specific PLCs and can confirm if the "memory only" claim holds true? Thank you.
Siemens explains that the "P" in programming denotes real-time writing, bypassing internal images. This fact has been tested and proven in high-speed applications. I once had to step in and work on a system due to illness where the original supplier did not use a high-speed card. I created a function block that was called multiple times in OB1 using PIW instead of IW, achieving great results.
While both PQWs (Process Quantization Word) and QWs (Quantization Word) can be used in Analog Output Modules, there's a notable difference between them. PQWs include process data and status information, making them more nuanced inputs, whereas QWs are simply the process data. If you choose to use QW only, you'll technically be omitting the status information. However, in majority of usual operational scenarios, QW should suffice. Just bear in mind that in doing this, troubleshooting could become a little trickier without the added status details provided by the PQW.
Absolutely, it can be a bit perplexing at first. PQW and QW both pertain to the addressing concepts in PLC programming. PQW allows you to control individual bits, hence providing more granular control. By contrast, QW represents an entire word of data. You can certainly use QW instead of PQW for controlling an Analog Output module, however, you would be dealing with a whole word (16 bits) instead of individual bits. Depending on your exact scenario, you might find one more suitable than the other. They both provide similar functionality in a broad sense, but the difference in bit-level control could be considerable in certain applications.
While it's true that PQW is displayed as the default setting, you can absolutely use QW as an alternative. In fact, they both work similarly with a little difference. PQW modules generate an output value in predictive control whereas QW modules only provide direct quantity output. While PQW is generally better for complex machinery like PLCs where reaction time is crucial, QW may be more efficient in simpler systems due to its directness and simplicity. Though one needs to keep in mind that these are essentially different modules serving similar purposes in different operation environments.
✅ Work Order Management
✅ Asset Tracking
✅ Preventive Maintenance
✅ Inspection Report
We have received your information. We will share Schedule Demo details on your Mail Id.
Answer: 1. Why does the Edit Symbol of an Analog Output module in Simatic Manager display PQW instead of QW? - The Edit Symbol in Simatic Manager defaults to displaying PQW for Analog Output modules.
Answer: - To use QW instead of PQW in Simatic Manager for Analog Output modules, you can make the necessary changes in the settings or configuration options.
Answer: - Yes, using QW instead of PQW in Simatic Manager for Analog Output modules should provide the same functionality. It's primarily a display preference that does not affect the module's operation.
Join hundreds of satisfied customers who have transformed their maintenance processes.
Sign up today and start optimizing your workflow.