Restoring an old model Tesa Electronic indicator

**RayG** · 13th February 2015, 02:04 PM

I bought this particular meter at a Gray's auction last year, and it came with wires dangling out of the battery compartment, and what looked like a dc plug connector for a plug pack...

The meter was originally designed to use 4V Mallory TR 233R Mercury batteries, but they haven't been made for years.... probably because of the mercury issues. So I decided to replace the mercury battery with a 3.7V lithium, and after checking the standard dimensions for a SAFT 25500 lithium battery, it would be a perfect fit. But the chinese 25500 battery I bought off ebay was 3mm longer than the standard said it should be, and wouldn't fit the battery compartment.... back to square 1.

If I could get a SAFT VL25500 the problems would be over, and I'd have a working meter... no such luck.

I eventually found a lithium thionyl chloride 3.7 Tekcell that was the standard C cell dimensions, so when it arrived I removed the dangling wires and cleaned up the battery contacts.. and away it went.. The Lithium thionyl chloride battery although it's the right size, it's not rechargeable, they are mostly used for memory backup systems and very low current applications.

Restoring an old model Tesa Electronic indicator-img_0967s-jpg

Restoring an old model Tesa Electronic indicator-img_0967s-jpg

The standard C cell, vs the Chinese C Cell

The TekCell C cell size is a whopping 8500 mAh capacity, so I thought I'd measure the power consumption, and see how long the battery will last.
The meter drew, 3.4 mA when on, and still drew 2 mA when the front panel switch was off... strange.. time to look inside.

Restoring an old model Tesa Electronic indicator-img_0963s-jpg

Restoring an old model Tesa Electronic indicator-img_0963s-jpg

Some idiot had wired up a TO92 3 terminal regulator with some 10 turn trim pots, no doubt to regulate the voltage from the plug pack they were using..
Well at least they protected the meter from overvoltage damage..

After removing all the extras and re-wiring it as per original, the power consumption dropped back to a comfortable 1.7 mA and zero when switched off.

Restoring an old model Tesa Electronic indicator-img_0965s-jpg

Restoring an old model Tesa Electronic indicator-img_0965s-jpg

So calculating the battery life, that's 8500 mAh / 1.7 that's about 200 days at 24 hours per day, If I remember to switch it off each time, it should last a few years.

Restoring an old model Tesa Electronic indicator-img_0968s-jpg

Restoring an old model Tesa Electronic indicator-img_0968s-jpg

One of the nice feature of electronic indicators, when compared to the mechanical indicators is the long sensing range and selectable sensitivity,

Ray

**GuzziJohn** · 13th February 2015, 03:19 PM

Originally Posted by RayG

Ray

Next time you measure current drain could you use something with a little more accuracy

Some of us have enough trouble with the mA range but resolution to 100'ths of a micro amp. Thats something else.

John

**chambezio** · 13th February 2015, 05:23 PM

Dumb question, (comes easy for me) what will you be using it to do?

**Techo1** · 13th February 2015, 05:47 PM

Those old Tesa's are very nice Ray, I used them a lot back in the 80's.

**.RC.** · 13th February 2015, 06:00 PM

What is the minimum resolution on them? The dial is not very informative..

Do you have any level type indicators with it or just the straight push type...

**Techo1** · 13th February 2015, 06:17 PM

Originally Posted by .RC.

What is the minimum resolution on them? The dial is not very informative..

Do you have any level type indicators with it or just the straight push type...

On the inch scale: Zero to 30 = 0.0003" with the dial in the .3 position. Zero to 10 = .001" with the dial in the 1 position,
There was a lever type attachment available.

**.RC.** · 13th February 2015, 07:55 PM

So each division is 0.00002" on the finest resolution.. Or roughly half a micron...

**RayG** · 13th February 2015, 08:20 PM

Originally Posted by .RC.

So each division is 0.00002" on the finest resolution.. Or roughly half a micron...

I only have the push type probes. I just double checked it against the Sony digital, the most sensitive scale is the 3 microns full scale, so each minor division on that scale is 0.2 microns. On the inch range it's the 0.1 setting, or 1/10 of a thou full scale, and 10 millionths per division.

Neither of those ranges are very friendly, if a fly lands 3 feet away the vibrations cause the needle to wobble...

The big advantage of this type of meter is being able to dial back the sensitivity to something more practical.

In answer to Chambezio's question what do you use it for, everything that you would use a dial gauge and DTI for, from dialing in a job on a 4 jaw chuck on the lathe to measuring run out on a chuck, tramming a vise on the mill etc etc.

GuzziJohn, I inherited that Yokogawa 7551 meter from a previous life where we did a lot of sensor interfacing type work, and it's still my favourite bench multimeter, even though it's long overdue for a calibration check.. as it happens, now years later I'm finding the low current ranges perfect for nano power type microcontroller applications.

Ray

**Techo1** · 13th February 2015, 08:28 PM

Originally Posted by RayG

I only have the push type probes. I just double checked it against the Sony digital, the most sensitive scale is the 3 microns full scale, so each minor division on that scale is 0.2 microns. On the inch range it's 1/10 of a thou full scale, and 10 millionths per division.

Ray

Yes, I didn't see the ".1 " setting.

**BaronJ** · 14th February 2015, 07:12 AM

Hi Ray,

Nice instrument.

At 1.7ma current consumption, you could use three coin cells as a power source. Add a diode in series for reverse polarity protection.

Mind you, I've done the regulator trick and used a wall wart before now.

**RayG** · 14th February 2015, 01:09 PM

Originally Posted by Techo1

Those old Tesa's are very nice Ray, I used them a lot back in the 80's.

One nice advantage I discovered is the ability to position the display independently of the probe, so that when tramming the mill, you don't have to lean around to see the dial like you would with a normal dial gauge. Also the probe tip can get into tighter spaces.

But the biggest plus is the selectable sensitivity...

In case anyone was wondering here is what it looked like before the clean up . http://www.graysonline.com/lot/0020-...nch?redirect=0

Ray

**Anorak Bob** · 15th February 2015, 09:38 AM

Now you just need one of these Ray.

http://www.ebay.com.au/itm/111292931...701%26_rdc%3D1

BT

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