S7-1500 Web Server vs S7-1200 Web Server Response Time

Hi guys! This is my "problem":

I lent to a customer a S7-1200 CPU to test its web server side. Following some online guides I built a RESTful API to which the customer can read and write the "hosted" variables. The customer is reading and writing on the json custom web page via https programming (that I know nothing about) and he asked me if I could add the user/password to the web server to test its response time.

A single "cycle" of calls consists of 4-5 requests and answers: login - read values - write values - read new values - logout.

Now the customer said to me that this "cycle" takes too much time, and he wanted to know if the S7-1500 CPU had better response time than the S7-1200.

I looked around a bit but I found nothing, I know that there are some S7-1500 CPUs that already have an API interface and I think that I'll suggest to use that, but I was still wondering if someone had any experience or opinions about the response time of the two series.

Thanks in advance, Ryan

Hello UTE_GAW,

please consider the main and load memory of the S7-1500 CPU is higher than by the S7-1200 CPU. The S7-1500 CPU Includes the simple functionality of S7-1200 and meets special demands for performance, flexibility and networkability.

Regarding to improve the performance see also the FAQ:

How can you improve the performance in STEP 7 (TIA Portal) and in the S7-1200/S7-1500 CPUs?
https://support.industry.siemens.com/cs/ww/en/view/37571372

With best regards
Cicero

Hello

What do you mean with to slow?

What is your current response time per request?

I've written a python script that communicates with my et200SP Webserver and i get an average response time of 0.5s per api call. It also doesn't matter how much (i tested from 1 to 10000 integers) data tags i request, it's always the same response time.

Kind Regards

VeulemansJens

Hello

What do you mean with to slow?

What is your current response time per request?

I've written a python script that communicates with my et200SP Webserver and i get an average response time of 0.5s per api call. It also doesn't matter how much (i tested from 1 to 10000 integers) data tags i request, it's always the same response time.

Kind Regards

 Hi VeulemansJens!

Too slow means that for the operation it needs to do it takes too much time compared to what normally a response time is. My customer and I saw that for a full request-cycle it takes 8 to 10 seconds to operate 5 requests.

I don't really know the response time per request, if I remove the passowrd access everything speeds up, and the request is handled as normally as you'd expect.

I don't know if there's an API on the et200sp, but surely there isn't on a S7-1200 and I' not programming in python but in php, I already know that it doesen't matter if it's a bit or a string that the program is requesting.

An et200SP is 1500-series CPU so it has a built in API. a request to this API takes 0.5s to get a response with authentication. 

If you use an s7-1200 at the moment i would go to a ET200SP, switching to an s7-1500 would be overkill.

I'm not sure how fimiliar you are with programming and API's but the 1500-series have an RPC API so you can make a url call from any programming language and you will get a response. doesn't matter if it's python, C#, PHP, JS,....

I tought you've built a RESTFul API on a seperate server and have that server communicate with the PLC over TCPIP or PUT/GET or something but i'm starting to think you've just made something that uses AWP commands, is that correct? This is indeed a very slow method and is not the way to go. Could you clearify your setup? 

Could you explain in detail what you mean with:

"I lent to a customer a S7-1200 CPU to test its web server side. Following some online guides I built a RESTful API to which the customer can read and write the "hosted" variables."

So let's clear out on which way you are communicating with the plc before we can continue.

On another point: i don't think there is anything wrong with asking somebody what they mean with "to slow". If you want good help you need to be detailed and specific. By being rude you don't get anywhere...

VeulemansJens

An et200SP is 1500-series CPU so it has a built in API. a request to this API takes 0.5s to get a response with authentication. 

If you use an s7-1200 at the moment i would go to a ET200SP, switching to an s7-1500 would be overkill.

I'm not sure how fimiliar you are with programming and API's but the 1500-series have an RPC API so you can make a url call from any programming language and you will get a response. doesn't matter if it's python, C#, PHP, JS,....

I tought you've built a RESTFul API on a seperate server and have that server communicate with the PLC over TCPIP or PUT/GET or something but i'm starting to think you've just made something that uses AWP commands, is that correct? This is indeed a very slow method and is not the way to go. Could you clearify your setup? 

Could you explain in detail what you mean with:

"I lent to a customer a S7-1200 CPU to test its web server side. Following some online guides I built a RESTful API to which the customer can read and write the "hosted" variables."

So let's clear out on which way you are communicating with the plc before we can continue.

On another point: i don't think there is anything wrong with asking somebody what they mean with "to slow". If you want good help you need to be detailed and specific. By being rude you don't get anywhere...

I uploaded a web server project on my 1200 CPU that contains an "api.io" page, the only thing that page has on it are the AWP commands of the "hosted" variables and the variables themself with some formatting to form a .json file.

Now that a .json file is accessible the customer with his program can interact with it. And by that I mean that he can read/download the .json file and even write in it new values.

So the problem is that: in his program my customer need to send an access request to the web server (not the user's custom pages), then wait for the acces, then go to the "api.io" page, read the .json, write the .json and then re-read the values to know that the variables are the new ones, then disconnect.

So the PLC in this project is totally passive, is the customer who can read/write directly into my Web Server.

The customer has no intention to take the API route because that would mean a program change for him, so I was wondering if someone had any experience like this on a CPU1500 or at least that wasn't a 1200 series.

On another note I'm sorry if I sounded rude, it wasn't my intention and I'm very glad someone is interested in helping me out, thanks.

I've worked with the AWP method on 1200s, 1500s and et200SPs and the speed is as slow on all of them. Siemens put it also somewhere in one of their webserver manuals that this method could become slow

Keeping the exact same method wouldn't be faster with a different model or series. Your customer probably won't like the answer but if he wants faster speeds he'll need to switch methods. But convincing a customer to do the obvious and necessary thing is the hardest part haha.

Good luck!

VeulemansJens

I've worked with the AWP method on 1200s, 1500s and et200SPs and the speed is as slow on all of them. Siemens put it also somewhere in one of their webserver manuals that this method could become slow

Keeping the exact same method wouldn't be faster with a different model or series. Your customer probably won't like the answer but if he wants faster speeds he'll need to switch methods. But convincing a customer to do the obvious and necessary thing is the hardest part haha.

Good luck!

 Alright that's "good" news

Tomorrow I'll go to the customer and see if we can come up with something, if there are any changes I'll post them in this topic, so I'll let you know if something has changed (will it be my customer mind, or the PLC configuration).

Thanks again!

Last update for now, I found something that improved the response time.

Under Device Configuration -> Communication Load you can set the percentage of load the CPU is allocating to communications in the cycle. The CPU I was working with had the precentage set to 20% (standard), I maxed it at 50%.

The Response time dropped to 3 seconds, and since before it was at 8-10 seconds the results are there. It's still a slow communication and it can be done in many other (faster) ways, but at least now I know that there was something I could do.

Hello Ute_Gaw,

i think that a faster response time it's possible.

But your customer, have to use the S7 protocol on the own application.

kind regards