How to probe the parameters of a mechanical encoder

[Hoi Wong]

The mechanical encoder on my Wavetek 75 is broken (mechanically) but it's
too hard for me to solder anything to the tiny remains in the broken pins.
In this case, I need to buy a new encoder.

Is there a way to probe the parameters such as Pulse Per Revolution, coding
(gray, 2-bit, binary, BCD)? I can still stick my multimeter probe to it.

Thanks.

Cheers,
Hoi

 

[Dave Platt]

The mechanical encoder on my Wavetek 75 is broken (mechanically) but it's
too hard for me to solder anything to the tiny remains in the broken pins.
In this case, I need to buy a new encoder.

Is there a way to probe the parameters such as Pulse Per Revolution, coding
(gray, 2-bit, binary, BCD)? I can still stick my multimeter probe to it.

Almost all of the rotary encoders I've seen used for instrumentation
control, whether mechanical or optical, use a 2-bit Gray code system.
The mechanical ones are simple contact-closure types, while the
optical ones (continuous or detented) use an LED to illuminate a pair
of open-collector (active-pulldown) phototransistors.

If it's a mechanical encoder, you should be able to use an ohmmeter to
"beep out" the connections. Turning the control one detent position
would cause one of the two switches to change state, while the other
remains unchanged. Turning the control another detent position in the
same direction will cause the second switch to change state while the
first remains unchanged.

Each output is usually one full pulse cycle per four detent positions.
If the control isn't detented, you'll have to count up the number of
pulses in some measurable angle of rotation and then multiply up to
360 degrees.

If it's a detented optical encoder, the same rules apply, but the
"switches" will remain open to external measurement unless you're
supplying the necessary current to the LED. There is often (but not
always) an internal current-limiting resistor to provide the necessary
LED current with a 5-volt supply.

Do you have a service manual / schematic? This could make it clearer
whether the encoder is mechanical or optical in nature.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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