help to replace tacho generator

Thread Starter

ss.achary

Joined Oct 27, 2015
28
I would like to replace an dc motor tachogenerator with encoder... But the motor is controlled by drive which has only tacho input for feed back... So I have to fix an encoder with analog output... Tacho spec: 10v/1000rpm..
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
I assume you have an older DC drive that has a DC tach feedback, an encoder is generally digital, what context are you using the drive in? Simple open loop velocity drive or do want or need to control it with a PID loop etc?
Max.
 

Thread Starter

ss.achary

Joined Oct 27, 2015
28
I would like to modify an encoder with analog output similar to tachogenerator... This should work in DC drive that has a DC tach feedback...
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
Incidentally DC tach's are no longer used in current positioning drives, there is a single PID loop that is returned to the trajectory planner or control, typically using torque mode rather than velocity mode control.
So if I understand you correctly, you want to use a DC tach as an encoder of some kind?
Is this an existing system or are you designing something?
The full story helps, including any details of present equipment.
Max.
 

ScottWang

Joined Aug 23, 2012
6,819
The tachogenerator is output an analog voltage, but the encoder output two phase pulses, so you may need two sets of F to V(the Frequency-to-Voltage converter), those provided two directions as forward and reverse, if you don't need the reverse then you just need one set of F to V.
 

Thread Starter

ss.achary

Joined Oct 27, 2015
28
The tachogenerator is output an analog voltage, but the encoder output two phase pulses, so you may need two sets of F to V(the Frequency-to-Voltage converter), those provided two directions as forward and reverse, if you don't need the reverse then you just need one set of F to V.
Please provide me full block diagram for it... Encoder - decoder - up/down counter-f/v converter
 

Thread Starter

ss.achary

Joined Oct 27, 2015
28
WP_20151029_12_35_13_Pro.jpg use this encoder instead of tacho... And connect the output of encoder to the same drive... I need help in replacing it....
 

ScottWang

Joined Aug 23, 2012
6,819
You can see the encoder pulse, you have to design a pulse detector for encoder forward and reverse, maybe the output as A = pulse, B = low when the encoder forward, and the output as A = low, B = pulse when the encoder reverse.
rotary_encoder_phase.jpg
Source.

And the output of your block diagram, the output of F/V as two 0~5V, how do you use these two voltages to control the motor?
 

Thread Starter

ss.achary

Joined Oct 27, 2015
28
You can see the encoder pulse, you have to design a pulse detector for encoder forward and reverse, maybe the output as A = pulse, B = low when the encoder forward, and the output as A = low, B = pulse when the encoder reverse.
View attachment 93684
Source.

And the output of your block diagram, the output of F/V as two 0~5V, how do you use these two voltages to control the motor?
Please provide me a alternative method...
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
I doubt you are going to be able to use that quadrature encoder to input to the drive, you would need to convert to a linear analogue signal.
Is there any reason you are not using the original tach, if built in and is defective, it will be easier to fit an external DC tach, I have done this in the past.
Max.
 

Thread Starter

ss.achary

Joined Oct 27, 2015
28
I doubt you are going to be able to use that quadrature encoder to input to the drive, you would need to convert to a linear analogue signal.
Is there any reason you are not using the original tach, if built in and is defective, it will be easier to fit an external DC tach, I have done this in the past.
Max.
Sir the tacho coil is costlier... If I use encoder it would be less cost and easy to fix it in motor...
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
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.
 
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