SRF-113 Impedance Selector Switch test/verify question

[Raoul Duke]

This switch seems pretty common nowadays and after a quick search here and on Google - I still have a question someone(s) here may be able to shed some light on.

Is there a way to bench test this switch to verify the data sheet info?

The sheet shows the switching pattern and gives a reference; i.e. “circuit diagram shows the switches as viewed from the terminal side with the shaft fully turned in the counter-clockwise direction”

Maybe I’m overthinking this - but is that counter-clockwise as stated or CCW when viewed from the normal operating side? The reason I ask is that when referring to potentiometer lugs, CW and CCW are always referenced in relation to the normal operating side - leading me to wonder if there’s a simple bench test to verify?

Tried continuity from each terminal to the “out” terminal, but everything seems to have continuity regardless of switch position. There is a “flat” on the shaft as well - which leads me to wonder if there’s an implied directional reference to match that?

IMG_0302.png

Any info is appreciated! Thanks all!

[martin manning]

Is there a way to bench test this switch to verify the data sheet info?

You should be able to measure continuity or ohms from the 0 terminal (pole) to the 1, 2, 3 terminals. 1 should be closed CCW, 2 Center, 3 CW.

[Raoul Duke]

Thanks, that’s what I thought as well Martin - but I get continuity between pole “0” and all three other poles (individually) no matter where the switch is. The resistance reading is .6R on each individually also.

When testing, I’m in resistance mode on the DMM and I’m keeping one probe on “0” while cycling through the switch positions and other poles sequentially. Am I doing this wrong? I tried two other switches in working amps as well and got the same results. Now I’m wondering if I wired them all incorrectly. I know center is center - so I guess that’s something anyway, lol.

There’s got to be something I’m missing here…

[Astronomicum]

If the selector is wired to the OT, then those readings make sense. If so, lift the OT wires and try again.

[Raoul Duke]

Understood and will do Astro. I thought about that after the fact and wondered if it would make a difference. My inexperience showing again
Thanks, much appreciated - I’ll report back.

[martin manning]

I thought you were looking to verify the connections with the switch on the bench. Indeed if it’s wired to the OT secondary the low resistance will make it look like the switch is shorted out.

[Raoul Duke]

I originally was Martin; then I got ahead of myself and wired it up. Then I started thinking about it and tried to test it in place thinking it was measuring the internal continuity regardless of the external connections.

I know I’m a doofus sometimes - but I’m really trying to drill in to understanding how things work - which sometimes leads to me drawing incorrect conclusions based on my lack of formal training.

Looking back on my notes, I somehow came to the conclusion that the flat on the control post “points” to the contact position - but I don’t remember how I got there - so now I want to understand this switch inside and out. All my builds using the same switch seem to be correctly wired; but again I want to verify just in case I did it wrong based on my mysterious conclusion.

Apologies for my “doofusness”, taking the switch out now and testing literally “on the bench”.

[Raoul Duke]

And of course - I take the switch out of circuit and it all makes sense. Contact engaged shows resistance, two not engaged show OL all the way around.

Coincidentally (?) the flat points to the contact engaged when the switch is oriented with lugs 1-3 in the up position.

Notes corrected to include “how I got there”. Don’t know how I forgot all this as my other builds with this switch follow the flat pointing pattern. Got to be the TBIs catching up with me…

Thanks again guys!