# help to replace tacho generator

#### ss.achary

Joined Oct 27, 2015
28
No s
Have you tried a small (cheap) DC motor ran as a generator, which is all the tach is anyway, just a refined one, if the original tach was 10v/1krpm then a DC motor with the same voltage should work.
i.e. 20v motor @2000rpm.
Most drives have a pot to calibrate the tach to fine tune it.
Max.
No sir I haven't tried.... Is it possible to fit an encoder....

#### ScottWang

Joined Aug 23, 2012
7,005
If you have the parts then you can try this circuit, I haven't try yet.

Joined Jul 18, 2013
22,857
No s
No sir I haven't tried.... Is it possible to fit an encoder....
For a lot less money and trouble, I would tend to try the DC motor first.
Max.

Joined Jul 18, 2013
22,857
If you have the parts then you can try this circuit, I haven't try yet.
He needs analogue signal, simulate a DC tach.
Max.

#### ScottWang

Joined Aug 23, 2012
7,005
He needs analogue signal, simulate a DC tach.
Max.
Did you see my posted in #6?

#### ss.achary

Joined Oct 27, 2015
28

#### ss.achary

Joined Oct 27, 2015
28
How can I convert this signal to analog....

Joined Jul 18, 2013
22,857
No s
. Is it possible to fit an encoder....
For around $10-$20 using a miniature DC motor might be the better candidate, you are going to have to convert to a analogue signal using the quad encoder.
Also there can be no delay or oscillation will result.
The Tach signal is summed with the command signal and the motor will accelerate until both are equal.
Max.

#### ScottWang

Joined Aug 23, 2012
7,005
How can I convert this signal to analog....
F to V.

If this is not a homework then I will move to -- The Projects Forum, is this ?

#### ss.achary

Joined Oct 27, 2015
28
F to V.

If this is not a homework then I will move to -- The Projects Forum, is this ?
Ya surely sir

#### ScottWang

Joined Aug 23, 2012
7,005

#### ss.achary

Joined Oct 27, 2015
28
will work with this circuit

#### ss.achary

Joined Oct 27, 2015
28
If I use digital potentiometer with required output config....

#### ScottWang

Joined Aug 23, 2012
7,005

#### ss.achary

Joined Oct 27, 2015
28
Will this work max sir and Scott sir......

#### ss.achary

Joined Oct 27, 2015
28
but this doesn't works with the dc drive I have shown in starting... It can measure rpm... But not the direction of motor

Joined Jul 18, 2013
22,857
You need bi-polar analogue signal, the LM2917 is same output regardless of direction.
Max.

#### ss.achary

Joined Oct 27, 2015
28
You need bi-polar analogue signal, the LM2917 is same output regardless of direction.
Max.
So what should I do sir

Joined Jul 18, 2013
22,857
You already have my opinion, Miniature DC motor!
Max.

#### strantor

Joined Oct 3, 2010
5,540
I encountered this problem several times back when I was servicing old machinery with DC drives. Replacing the drive itself to a newer one with an encoder input was usually cheaper than replacing the analog tach. But a handful of times there was a tach signal that went to more than one place. Like on an old cabling machine, where the main drive tach signal (100V/1000RPM) went not only the main drive, but also to two tape head drives, a gunk pump, a capstan, and winder. For situations like that, I needed a niche signal conditioner with encoder input and +/-300VDC output. I scoured the planet looking for such a thing and accepted that it does not exist. I had plans to build one, spent a lot of time on it, but never built it. I've since lost the circuit drawings I made. If you do end up making something like that, I'd be interested in seeing it. But if you can get away with replacing the drive for under \$100USD then that's probably the way to go.