3
\$\begingroup\$

enter image description hereI am trying to repair a very expensive manlift joystick. I had great luck soldering in a new potentiometer on a different machine and getting it back to work, but this other machine has a potentiometer that I have not seen before.

It has 4 pins total, three like a normal rotary potentiometer and then a fourth across from the other three pins.

It is a Clarostat U-10K-OHM Type EJ pot. It has another number stamped "99148B 9507"

Clarostat has been purchased by Honeywell, so I am having a hard time finding any catalogs or datasheets for this guy. Can anyone point me in the right direction or advise what the fourth pin may be for? Would replacing with a standard three pin pot be a possibility?

Thanks!

\$\endgroup\$
  • \$\begingroup\$ Well, that looks pretty much like the photo I posted- center tap 99.9% sure. Linear-taper extended-life 10K pot with a center tap (and whatever shaft and bushing length spec there is- I guess 6.35mm x whatever length). All that stuff was customizable if you bought a reasonable quantity. \$\endgroup\$ – Spehro Pefhany Jul 25 '16 at 18:54
5
\$\begingroup\$

I second Spehro in what he thinks it is: an heavy-duty pot with additional center tap.

TT Electronics seems to sell a product similar to the part sported in your photo (datasheet).

enter image description here

Here is an excerpt from the datasheet with the technical drawing:

enter image description here

And here is the electrical circuit:

enter image description here

Even if it is not what you are looking for, it may be a starting point.

\$\endgroup\$
  • \$\begingroup\$ Nice find. In stock at Digikey for < $15 USD. \$\endgroup\$ – Spehro Pefhany Jul 25 '16 at 20:03
  • \$\begingroup\$ That is perfect. Just ordered from Mouser 10.98ea for dust sealed. \$\endgroup\$ – Trey D Jul 25 '16 at 20:17
4
\$\begingroup\$

Not familiar with that series, but it appears to be an extended-life pot.

There are two possibilities for the 4th connection. The first is that it is a center-tap on the element. This might allow them to control the output at the neutral position of the joystick better. The second (and less likely one) is that it's a ground connection.

A quick test with an ohmmeter should settle the matter. Here is a picture of a center-tapped 10K pot. It would measure 5K from either end of the element to the opposite (center-tap) pin. The wiper would short to the center tap when in the center of rotation.

enter image description here

\$\endgroup\$
  • 1
    \$\begingroup\$ Since he is looking for a replacement, a quick check with a multimeter might not be a good option \$\endgroup\$ – PlasmaHH Jul 25 '16 at 22:11
  • \$\begingroup\$ @PlasmaHH even if there is not a working pot on another axis it would serve to rule out the ground option(but I think that's redundant given the photo the op added) \$\endgroup\$ – Spehro Pefhany Jul 26 '16 at 0:02
4
\$\begingroup\$

Four-terminal potentiometers were common at one stage on hi-fi volume controls to give automatic "loudness" control - see What's a potentiometer with four terminals in this schematic? - but these were logrithmic law and a joystick is more likely to be linear.

My guess is that it's a linear pot and that the centre-tap is used to provide a definite GND or reference to assist with a deadzone in the centre of the pot. This would be intended to prevent creep when the joystick is centred.

schematic

simulate this circuit – Schematic created using CircuitLab

I found a Clarostat brochure on Stephen Engineering and they seem to be handling the product now. They don't have any four terminal pots listed.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.