I have a SICK DFS20A-A2PBD065536 incremental encoder and I am powering it with 24V DC. When I rotate the shaft, I do not get any change in either A or B output signals (Its a quadrature encoder). We are certain the drawings are correct. My question is how protected are SICK encoders (or a industrial rotary encoder in general) to errors in wiring. We know we didn't apply 120V, and no welding has been done.

Encoder set for:

  • 60 PPR (pulse per revoloution)

  • HTL output (?Totem Pole? / output level based on input power (24V).

  • It worked when it left thet shop

  • We tried wiring it in the field, but it didn't work. (possible that we had error in wiring)

  • We brought back to bench to test, and it no longer works.


  • How sensitive are these encoders to miss wiring (shorting a pair of pins together, leaving a common open, 24V applied to the wrong pin. (In your experience?)
  • \$\begingroup\$ The datasheet says they are reverse polarity and short-circuit protected, so as long as you haven't applied more than 30V DC, then you should be OK on that front. Are you sure it's wired up correctly? \$\endgroup\$
    – NMF
    Commented Jan 13, 2021 at 19:34
  • \$\begingroup\$ Thank you kindly for your timely response! are there other common ways to burn out the encoder output channel than the ways they mention are protected against? I'm wondering if applying 24V to the output pin instead of the power pin would burn the device? I called SICK, but the tech. rep. I spoke with didn't inspire confidence... \$\endgroup\$ Commented Jan 13, 2021 at 20:02
  • \$\begingroup\$ There is a limit of 30s stated on the output short-circuit protection, which would be OK if you have an appropriately rated fuse on the 24V line that you may have connected to an output. Did you have a fuse installed? And if so, did it blow? \$\endgroup\$
    – NMF
    Commented Jan 13, 2021 at 21:21
  • \$\begingroup\$ Protected against output short to ground (as the datasheet specifies) does not necessarily mean it's protected against output short to +24. Possibly worse if there is no power applied when it happens. And there's the duration issue (though I expect their 30s spec would be conservative). There are certainly ways of making this kind of product bulletproof against wiring errors but they may not have implemented them. \$\endgroup\$ Commented Nov 22, 2023 at 6:04

1 Answer 1


I do use their products over 15 yrs, if there is a need for an encoder it's definitely SICK, no other is more preferred by me. They are low priced VS. competitors and very quality made. I had no issues over all these years, not on piece was changed yet.

You have to carefully read the manual and ask the service if there is something that you don't understand.

Pay attention on the output type:

  • HTL means PNP (positive) 24V output pulses,
  • open collector means NPN output - both these types suffer at high frequency and long cable (capacitance)
  • push/pull (totem pole) this is preferred by me, it allows long cable and hi. freq. The output voltage usually is the same as supply voltage
  • TTL this is high speed, differential output 5V (line driver, similar to RS485)

For your encoder it is stated that is HTL/TTL and has a default/factory setting as TTL, but as you said it was programmed for HTL.

Probably you have burned it by wrong connection, lesson learned. I also have burned one (not Sick) and until now the last one. You do need to focus on it when mounting, there are many colors, don't hurry. Usually I do use a selective electronic fuse. Siemens PSE200U


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