# help to replace tacho generator

Joined Jul 18, 2013
22,819
I would guess that if the OP does not want to try a simple/cheap DC motor solution, he may balk at a replacement drive.
It would also help to know the exact kind of machinery it is on, servo positioning? CNC? Open loop, simple velocity?
Max.

#### strantor

Joined Oct 3, 2010
5,528
I would guess that if the OP does not want to try a simple/cheap DC motor solution, he may balk at a replacement drive.
It would also help to know the exact kind of machinery it is on, servo positioning? CNC? Open loop, simple velocity?
Max.
Maybe his issue isn't with cost. Maybe he just doesn't trust your advice. We may never know; unless I missed something, he's just ignored your every post thus far.

Joined Jul 18, 2013
22,819
He posted a picture of an encoder he has, I think he may be determined to use it.
Max.

#### ss.achary

Joined Oct 27, 2015
28

#### ss.achary

Joined Oct 27, 2015
28
Sir they have did it... Y cant we...

Joined Jul 18, 2013
22,819
I see ±10vdc analogue for command signal but no simulated Tach?
Max.

#### strantor

Joined Oct 3, 2010
5,528
Interesting device there but it isn't an encoder (frequency) to voltage signal conditioner. It's a counter with an analog output. This is for positioning. Your analog output would correspond to rotor position, not rotor speed.

#### ss.achary

Joined Oct 27, 2015
28

Joined Jul 18, 2013
22,819
I see you appear to be determined to use a device in the $100's of dollars in place of exploring a precision miniature DC motor such as Pittman or Maxon for a tach for <$50.00 on ebay.
That unit BTW maxes out at 10vdc, so if your motor is 2k to 3k rpm it will not meet the required limit of 10v/1krpm.
Max.

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#### strantor

Joined Oct 3, 2010
5,528
That unit BTW maxes out at 10vdc, so if your motor is 2k to 3k rpm it will not meet the required limit of 10v/1krpm.
Exactly! There are more examples like this one. I have used the one he linked and it's a good product, but like all its competitors, it only deals in today's typical signals; 0-10V, 1-5V, 4-20mA, etc. Trying to find a product that actually simulates a DC tach, like the kind OP has (or worse, those that can put out upwards of 300V), well it's maddening. There's no such thing. And there should be, IMO.

Joined Jul 18, 2013
22,819
Trying to find a product that actually simulates a DC tach, like the kind OP has (or worse, those that can put out upwards of 300V), well it's maddening. There's no such thing. And there should be, IMO.
In the past there may have been a need, or now for legacy drive systems, but in the world of DC Servo's now, DC tach's are not used (torque mode now) , plus most servo's have gone to BLDC/AC so IF a application is needed for some kind of open velocity loop, the commutation pulses are used for tach purpose.
At least that has been my experience so far.
Max.

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#### strantor

Joined Oct 3, 2010
5,528
In the past there may have been a need, or now for legacy drive systems, but in the world of DC Servo's now, DC tach's are not used (torque mode now) , plus most servo's have gone to BLDC/AC so IF a application is needed for some kind of open velocity loop, the commutation pulses are used.
At least that has been my experience so far.
Max.
Right. Sorry, that was an unannounced continuation of my previous rambling in this thread about replacing legacy tachs on legacy machines with legacy drives, where the signal from the faulty tach goes to multiple destinations - those destinations sometimes being legacy purpose-made analog control cards for which there is no replacement. I've been in the situation before that I had to purchase a several thousand dollar special dual tach because without it, a complete retrofit of all machine controls would be required. In that unique situation (and I've been there more than once), such a niche high voltage signal conditioner would have been ideal. But there's no such thing. And I had plans to make one, but didn't follow through.

#### ss.achary

Joined Oct 27, 2015
28
Max sir my senior had tried with miniature dc motor... But it failed... If they fix miniature dc motor.. The drive runs it and shows tacho alarm..

#### larrydd

Joined Nov 4, 2015
3
Having worked - many years ago - as a senior service technician for a company that manufactured DC and AC drives, I recall that quite a few DC drives we sold used back EMF feedback (i.e. the DC output) to stabilize the speed. Admittedly this gives a lower performance than a tachometer, but in many applications was quite adequate. Perhaps this would work in this application. I've long discarded the diagrams, but perhaps someone else could help - if it would be useful to do so.