Optical rotary encoder and Osilloscope connections - Page 1
Forum section: electronics / repair

author: natsud2
author_rank: Newbie
timestamp: February 24, 2016, 06:24:38 am
content: Sorry if this is not the correct way to ask a question. I have 2 encoders...1 that I know is good working condition and one that I've tried to repair. I am now trying to use a 2 channel oscilloscope to compare the two encoders one at a time to make sure I have fixed the one. I am a novice in electronics and I also am not too familiar with Oscilloscopes just fyi. Also the encoder is the type that has A+ A- B+ B- Z+ Z- signals (differential line driver I think it's called) my problem is when I connect the Oscilloscope probes to the A and B channels I get the same signal on both channels. So I get a high signal at the exact same time on both channels...they should be 90 degrees out of phase. This happens on both my known good one and the one I tried to repair. I think it has something to do with the probes having a common ground? I am hoping someone could describe to me(or maybe a video) how to connect the 2 probes to the encoder or set the oscilloscope so that I can see the signals the way they should be(maybe a different way for triggering?). There are three pots on the encoder circuit board that adjust the pulse widths of each encoder channel that I need to make sure are set to equal widths(if that makes sense). I have attatched a pic of the signals I am expecting to see just for reference. Thanks for any info you could provide and plz remember Im no expert so I may need simpler instructions

author: Smokey
author_rank: Super Contributor
timestamp: February 24, 2016, 06:31:22 am
content: You have a data sheet or at least a part number for the encoders? How many lines per revolution?Typically A+, A- etc are the differential pairs for each channel. You can usually ground the - and just measure the + single ended for each.Z is typically the index track, so that should output one pulse per rev.You typically also have to supply your own power for incremental quad encoders.

author: natsud2
author_rank: Newbie
timestamp: February 24, 2016, 06:48:26 am
content: I have a pdf with some info not sure if it has what you need.The encoder is a BEI hs35 2048 pulses/rev ABZ channels 5-24v input and the output is same as input. I think when i put the channel 1 probe ground on the A- channel it shorts out the B- channel or something like that. The Z channel is just one pulse/rev but I only have a 2 channel scope. I power the encoder with a 12 volt battery because Im afraid of shorting the oscilloscope thru the power supply its my cousins scope and I dont wanna break it(cost more than I could possibly afford) ....It wont let me attatch the pdf because its too large so here is a link to ithttp://www.beisensors.com/pdfs/HS35-optical-incremental-encoder.pdf

author: Smokey
author_rank: Super Contributor
timestamp: February 24, 2016, 11:50:12 pm
content: Those look like really good encoders.You should be able to just use 5V for the power. That's a typical encoder supply voltage and fits the 5-28V range of these rugged encoders.For the scope connections:Tie both A- and B- to supply ground. Connect your scope probes to A+ and B+, with the ground clips on the same ground that A- and B- are on. Trigger on either channel.You shouldn't need termination resistors as long as you aren't spinning super fast.

author: natsud2
author_rank: Newbie
timestamp: February 25, 2016, 03:01:40 am
content: Ok I think that is what I am doing but it still seems like the common ground thru the probes is screwing with the signal. I have uploaded a video to youtube if you wouldnt mind checking that out maybe it will tell you more than I canhttps://www.youtube.com/watch?v=54enbfypJTM&feature=youtu.beThanks for responding

author: natsud2
author_rank: Newbie
timestamp: February 25, 2016, 03:39:43 am
content: here are a few pics. I think I can see a pattern of the short begining of the pulse is a channel turning on then when bchannel turns on the pulse steps to to full height then A turns off the signal lowers then b turns off and signal goes to 0. That seems like the ground of the probes are tieing both A and B channels together and the signals are "transposed"on top of or "added" together if that makes sense....

author: natsud2
author_rank: Newbie
timestamp: February 25, 2016, 03:41:25 am
content: both probe grounds connected signal pic