Position feedback sensors - terminology

Hello to all,
I have watched the latest webinar “Introduction to Feedback Types” and would like to be sure about the correct terminology.
I have experience with Balluff Micropulse linear position transducers such as BTL0324 (BTL5-E10-M0150-P-S3). All application use analog feedback 4-20 mA.

For these Balluff linear position transducer we always use term MDT, but according to the terminolgy presented in the webinar MDT is actually a digital/pulse feedback setup.

Is it wrong to use term MDT with analog 4-20 mA feedback?
If I understood correctly SSI and MDT PWM can provide much better resolution that analog 4-20 mA feedback?

Thank you!

Hi Jasner,

Great question, It can be a bit confusing but generally here at Delta we refer to MDT transducers as transducers using PWM or St/St outputs, but they can also have SSI or analog outputs such as your own. In the webinar we talked about the definitions briefly, but it was easy to miss!

So it’s correct to use the term MDT with an analog transducer such as yours but probably the most descriptive to say analog MDT.

You are also correct in that SSI and MDT can provide better resolutions than the analog alternatives, if you have to option to choose for a new project, or just need higher resolution for better control we almost always recommend going with SSI!

David, thank you for the reply.
I wonder if the following setup is possible.
The control cabinet with PLC that has only analog input card, resolution 13 bits is about 400 or 500 meters from the analog MDT. Would it be OK to use Balluff SSI transducer and 500 m cable to the control cabinet and to install SSI/4-20mA signal converter inside the cabinet. Then, only a small portion of cable to the AI input card?

This approach could definitely work, the thing you’d need to watch out for is your max cable length is dependent on your clock rate. Here’s a nice chart showing approximations:

And our available clock rates on the RMCs:

You can see this would be doable assuming your sensor can work with the frequency as well. It looks like and RMC200 or possibly an RMC75 would be able to get you the length you need.

Also, here are the help topics I grabbed those images from if you’d like to dig deeper:


Delta Computer Systems Website