On Off switch – Digital Calipers

[Neil WyattModerator @neilwyatt]

[Neil WyattModerator @neilwyatt]

I just found five spare minutes, so I thought I'd test the old saw that the on/off switch on digital calipers (etc.) doesn't do anything.

I have a digital multimeter with a 20 uA range. It's only a cheap one so the resistance on this range is pretty high – putting it in series with the cell caused the display to flash as it does if the battery is flat. The current consumption went consistently between 1.20 and 0.8 uA in time with the flashing. I would guess that with the display on constantly the consumption would be consistently about 1.2uA.

When switched 'off' and the display clear all the time the current was much steadier at around 0.6 – 0.7 uA.

So, although the caliper still takes current when it is 'off' it's only a bit more than half the 'on' current.

The short answer is, yes it is worth switching off, especially in cold weather when button cells can go flat much more quickly.

Neil

[Ed DuffnerParticipant @edduffner79357]

I always try to switch off my Vernier calliper but quite often forget the vertical scale on the milling m/c. Is it known why the on-off switch doesn't switch off the current completely?

[jason udallParticipant @jasonudall57142]

Anyone know the self discharge of the button cell ( in these devices?)

I ask since in a previous life have designed circuits pushing the self discharge limits ( ie comparable)…of the batteries powering them

[Neil WyattModerator @neilwyatt]

Yes, the callipers still register any movement made with the display switched off, so you don't have to re-zero the display when you switch on, even if the calliper/mike/slide gets 'twiddled'.

Neil

[jason udallParticipant @jasonudall57142]

As to why this doesn’t completely power down the device…
A few possibilities. .
Cheap ness..slide switch..moving part..more expensive than a pushbutton. .

Function. .stay powered to hold reading.. power down display to save some power. .

But your guess

[Ed DuffnerParticipant @edduffner79357]

Of course, thanks Neil.

[John Stevenson 1Participant @johnstevenson1]

Jesus H Christ with a Bridgeport.

These button cells cost 70p and last a year.

So that works out to 0.0019178 pence per day.

Mind you if you really want to make a saving, take 3 years off and only work the leap year and it works out to 0.0019125 pence per day.

[Engine BuilderParticipant @enginebuilder]

I never switch off my Mitutoyo one and it lasts about a year like John say's.. The one I had as a gift from ME subscription goes flat all the time even though I turn it off when not in use. You get what you pay for?

[Richard MarksParticipant @richardmarks80868]

I had a cheap vernier that was very good in itself apart from an auto power off system that flattened batteries all the time, I now have a Mitutoyo that has an off switch, I also have a cheap plastic vernier that will give me a rough and ready reading and so far has saved me from using the best one except for special jobs, on the back of the workshop door is a LARGE sign telling me to check ALL displays are off and to make sure the dust extraction vac is off, the reason for the dust extraction to be off is because it uses a sensor to switch on when any of the woodworking tools are powered up, the thyristor in the vac has before gone faulty and has left the vac running on its own for hours on end, I only found out when my neibhour wondered why I was working late at nights in the workshop, there was another fire at the Cutty Sark recently and it was put down to a vacuum cleaner being left on by the staff, they may well have used it as a dust extractor for power tools and as it is switched on and off by the tool it may well have been inadvertantly left in a live state for long periods.

[Neil WyattModerator @neilwyatt]

John, you are being ripped off. I get ten for £1 in the bootsales, with a couple of dozen in other sizes thrown in. Life in cheap callipers, about a year.

Those who love proper on/off switches need to remember these are the same read heads as used on digital machine scales. the ones on my mill are now remotely powered, which means I must remember to leave the readout powered up if I need to keep the scales set overnight.

Neil

[John HaineParticipant @johnhaine32865]

A couple of orders of magnitude off on that calculation! 70/365 = about 0.2 pence per day.

[FMESParticipant @fmes]

Posted by Ed Duffner on 26/10/2014 14:39:49:

Is it known why the on-off switch doesn't switch off the current completely?

To maintain the memory position

[John Stevenson 1Participant @johnstevenson1]

Not being ripped off I get good quality ones,

One thing with these calipers you need SR batteries not LR, many times LR's won't read correctly.

I think it's something to ge with SR's ar 1.3v and LR's are 1.2 or something and that tiny difference makes all the difference.

John H, you are correct with your calculation. I now need to find more empty pop bottles to take back.

[Ed DuffnerParticipant @edduffner79357]

Posted by John Stevenson on 26/10/2014 15:37:48:

Jesus H Christ with a Bridgeport.

These button cells cost 70p and last a year.

So that works out to 0.0019178 pence per day.

Mind you if you really want to make a saving, take 3 years off and only work the leap year and it works out to 0.0019125 pence per day.

Convert it to 3 phase AC and run it off an inverter.

[Bill PudneyParticipant @billpudney37759]

First up, I hate electronics and everything to do with electronics, including batteries. I'm not wanting to upset anyone with my twisted opinion, I know that lots of people like electronics stuff, but I'm not one of them.

When I had to work for a living, one of the things that I had to do was to design the mechanical aspects of military electronic equipment. Basically the metal boxes that protected the electronics from heat, cold, dust, water etc. One of the things that I learn't really quickly was that slide switches are not reliable, even so called good quality ones. We always used pushbutton or toggle type switches.

So apart from my dislike of electronics, I try not to use anything with a slide switch. This tends to mean that the only thing in my workshop with a slide switch is a calculator (Casio) bought in 1980, which has taken me through 20 years of study, 35 years of work, without being switched off. I just let the thing "power down" automatically. It's now on its third battery!

cheers

Bill

[Gordon WParticipant @gordonw]

I bought my digital "vernier " about 10 years ago, the man threw in a spare button battery. I'm still on the original battery. Does not get a lot of use and always off when not in use. Am I just lucky ?

[Neil LickfoldParticipant @neillickfold44316]

I use SR44 or 357 cells for my Calipers. The SR 44 and 357 are Silver Oxide batteries. They have about 170 or so mah capacity, compared to the LR44 that has anywhere from 60 to 110 mah depending on manufacturer.

The 357 have a lower internal resistance and are used in camera's. So for me it is easier to just buy 1 part and use it in all my devices.

I do not bother turning off my calipers as they are the older type that need zeroing when started, apart from the newer solar powered one. I get about 18 months on my caliper brought in 1987, but only get about 1 year with the 2003 brought caliper. Not sure why the newer one uses more power than the older one. It may be that the newer 2003 one remembers it's last zero setting, Either way, the saving of turning them off is just not there to me, compared to the convenience of just using it.

Neil L

[Gordon WParticipant @gordonw]

Just used my caliper mentioned above- no makers name, battery is SR44 @ 1.55V , it says.. Still working!

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