To convert Quadrature Encoder signals to Tachogenerator signals

[Babar]

Hi All,

I am using a DC drive which takes analog tacho signals
to run a Fanuc DC Motor which only have a Digital
Encoder , so I need to convert the Encoder signals to
Analog voltage to use this as Tacho feedback. Can
anybody help me by suggesting a simple circuit?

Regards

Babar

[Al_The_Man]

Are you using later type Drives? As modern ones run a DC motor in the torque mode, so the tach can be eliminated.
If you really need a tach, there are several simple dedicated IC's that will produce digital to analogue signal ones I have used in the past is the National LM2907 the IC manufacturers have application sheets on their sites.
You will only need to use one of the encoder channels i.e. A or B.
Of course, you will also need the encoder for feedback in a CNC system.
Al.

[unterhaus]

Al, don't the tachos go negative? Seems like you still need both channels to tell what direction you are going in.

USDigital has a box that does this, it's not particularly cheap.

[Al_The_Man]

Originally Posted by unterhaus Al, don't the tachos go negative?

Yes Your right of course, I fired this off in a hurry this morning, and realised it when thinking of it later.
It requires it more sophisticated DtoA than the national IC.
I think I have the circuit somewhere , I will try and dig it out tonight.
Al.

[Babar]

ACtually this is the main problem , to get the -ve sign. For this I need to have a circuit which can convert the Quadrature Encoder signals to the step and Dir signals , then the Dir signal can be used for changing the sign of the analog output voltage. For Quadrature Encoder to the step and Dir signals I tried the cicuit attached , but it didnot worked, I am getting pulses on the Dir output instead of getting high or low signals....