AutoGen_8564066

what is difference between MW and MD

MW is 16 bits long, MD - 32. 

Hello.

You are using the S7-200 programmed with Step7 Microwin. It is important that you mention that and not leave it for volunteers to guess. The S7-200 works a bit different than other Siemens PLCs. Also note that there is an "S7-200 Smart" which is also not exactly the same.

Best to also not write your query as if it is a phone text message (DM). Details are missed there. But thank you for putting down a screen capture.

You have M-memory and V-memory to work with. There is much less M-memory. M0.0 is a bit that is in MB0 but also MW0 and MD0. The B W and D indicates the sizing but it overlaps so that MD0 contains M0.0 to M3.7 / MB0 to MB3 and so on. 

It is worth your time studying the manual: [S7-200 System Manual]. The memory concept is explained there.

Then when it comes to scaling - best to review the specifications for the signal card as given in the manual (linked above). Also review a more product specific link: [How can you scale analog values with S7-200 in conjunction with CPU224XP and expansion modules EM 231, EM 232 and EM 235?].

Are these notes of help to you?

[ EDIT ]

About your application - yes you may need to use an analog output. But it may even be possible to use digital outputs. It depends on the control philosophy you are following. 

Assuming you have a cooling fan driven by the motor. The fan cannot run if the target temperature is higher than the measured temperature. The fan do run if the target temperature is lower than the measured one. How much difference may determine if the fan runs slow / medium / fast (x3 outputs).

You need to decide the method of control. PID / Fuzzy logic / Rule based / Model predictive ..