On Wed, 14 Nov 2012, Viesturs L?cis wrote: > Date: Wed, 14 Nov 2012 00:28:13 +0200 > From: "[UTF-8] Viesturs L?cis" <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] Differential signal from encoders > > 2012/11/14 Peter C. Wallace <[email protected]>: >> >> You can do the whole encoder interface with a 26LS32A chip (4 channel RS-422 >> receiver) > > Thank You, I did not know that such a chip exists with several channels in > one. > I just checked - even our local electronics supply store have them in > stock (at least that is what their homepage says). > >> Here's a sample schematic >> >> freeby.mesanet.com/422enc.pdf > > What are those 2 capacitors and diodes for? >
Capacitors are for high frequency bypassing the power to the 26LS32 chip. The VCC =5V power may be on relatively long lines from the power source = inductance. Without the capacitors, the 26LS32 chip will generate noise spikes in the power supply every time its outputs switch. If these noise spuke are large enough, they will cause data errors in the outputs. One diode is an LED (power on) the other is a reverse protection diode if you are prone to connect power backwards (I am) > >> On the other hand TTL may be OK if your count rates >> are not too high. >> >> (so you can set the encoder digital filter to reject HF >> noise) > > Could You, please, explain, what does TTL signal has to do with high > or low count rate? Most noise that causes encoder count errors is inductively or capacitively coupled into the encoder wires becuse of the LR ratio for inductive coupling and RC ratio for capacitive coupling, the noise tends to be short spikes in the 100 nS to 5 uS region. This means that if you do not have very fast encoder signals, this noise can be filtered out. > Motors have 1000 CPR encoders and are rated for 3000 RPM, so the count > rate should be up to 50 kHz. if these are indeed 1000 CPR (250 line) thats correct, but if they are 1000 line encoders (4000 counts per rev) max count frequency would be 200 KHz > > And how do You mean to set the encoder digital filter? I am missing > the moment of where am I supposed to have one. > All hostmot2 encoder counters have digital filters on all inputs (A,B,Z). The pass frequency of these filters can be set from MHz down to Hz Unfortunately there is not a convenient HAL parameter to set the filter time so it must be done using the raw-write facility. > -- > Viesturs > > If you can't fix it, you don't own it. > http://www.ifixit.com/Manifesto > > ------------------------------------------------------------------------------ > Monitor your physical, virtual and cloud infrastructure from a single > web console. Get in-depth insight into apps, servers, databases, vmware, > SAP, cloud infrastructure, etc. Download 30-day Free Trial. > Pricing starts from $795 for 25 servers or applications! > http://p.sf.net/sfu/zoho_dev2dev_nov > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
