Electrical – Output type of incremental rotary encoder

analogcontrol systemdigital-logicmicrocontroller

I have been trying to choose incremental rotary encoder for speed control of
three phase induction motor. My problem is that I am not sure what type of
output should I choose. There is following quadrature encoder interface
(please see the enclosure – signals from encoder are connected to terminals 1,2,3 in J9) on my control board. I don't know whether this
interface is intended only for incremental rotary encoder with open collector
output or it is possible to use different output types. Can somebody give me
an advice. Thanks in advance.enter image description here

I have found an encoder which is sufficient in terms of shaft diameter, supply voltage and output type. There are two parameters that are confusing for me in datasheet. The first one is maximum current requirements 180 mA. I suppose that this current is the maximum current that can be sink by the encoder's output transistor. In my case the transistor must sink \$\frac{5\,V}{4.7\,k\Omega}=1.06\,mA\$. Could this be a problem? The second confusing parameter is output load \$50\,mA\$ (including \$3.3\,k\Omega\$). What does this parameter mean? (\$\frac{5\,V}{3.3\,k\Omega}\neq50\,mA\$). Here is the datasheet of chosen encoder: enter link description here

Best Answer

Reading your schematic:

  • I see the A and B encoder phases which are standard for incremental encoder. - The "index" signal usually pulses once per revolution and may or may not be useful in your application.
  • The inputs have 4k7 pull-up resistors and this suggests it is designed for open-collector encoder. Since the pull-ups are connected to +5 V they will also support a 5 V TTL output encoder.
  • There are RC circuits to ground on your inputs. These seem to be performing a filter function and since the resistance is relatively high they won't affect the pull-ups significantly.

Usually encoders are used for fine position control and VSD/VFD induction drive doesn't do this very will. A more typical application is to fit a tachometer or encoder feedback to monitor motor speed. In this case either the A or B encoder output would suffice. In your case, however, the drive seems to be designed to accept A-B-Z type of encoder so you should be fine.

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