Philips cd100 servo board timer device

[geoff1234]

Does any one have any information regarding how to read the small glass cylinder device that is present on the servo board of a Philips CD100. Its not mentioned in the circuit or service manual. Its obviously measuring something but its not obvious how to read it. I attach a picture of it.

[Cobaltblue]

Its an elapsed time indicator.

Often used where items have a known or limited lifespan in industrial, commercial and military equipment.

The resistor along with the voltage set the "range"

Cheers

Mike T

[Jon_G4MDC]

Is that an attempt to meter Laser head lifetime?
Can't think what else...

[ms660]

This early one also has one fitted (scroll down quite a way):

https://www.dutchaudioclassics.nl/ph...rototype_nr29/

Lawrence.

[geoff1234]

Originally Posted by Cobaltblue

Its an elapsed time indicator.

Often used where items have a known or limited lifespan in industrial, commercial and military equipment.

The resistor along with the voltage set the "range"

Cheers

Mike T

Many thanks for the confimation - But how is it supposed to be read? There is a marker some way along the internal column but no indication which is the zero end. Also, is there any information anywhere about the calibration of the device?

[Red to black]

I have a feeling it wasn't intended to be read by the likes of us, more likely to have been calibrated within Philips themselves and only known by them how many hours have elapsed when it got to the end, Hitachi did similar with their early top loader Vcrs 8000/9000 series.

If you reverse the polarity to the component it counts down the other way

[Cobaltblue]

It's probably similar 120PC on this page

https://www.wiringdepot.com/Shared/S...ges/120-pc.pdf.

if we assume that its 4mA per hour and the supply is 5v that would give a full scale of approximately 570 hours the direction of movement is explained on the datasheet.

Doesn't sound a lot to me

We used the devices on military prototypes when I was just starting out.

Cheers

Mike T

[murphyv310]

Hi.
This was on SOME very early CD-100's that I found out later to monitor reliability. I'm pretty certain that select customers or perhaps Philips engineers or staff had these players. I have only ever come across one like this, (clearly remember it) many moons ago. There was a tie on label on the one I saw that said something like "only to be repaired by authorised Philips service agents" I never saw this on any other CD-100

[geoff1234]

Originally Posted by Cobaltblue

It's probably similar 120PC on this page

https://www.wiringdepot.com/Shared/S...ges/120-pc.pdf.

if we assume that its 4mA per hour and the supply is 5v that would give a full scale of approximately 570 hours the direction of movement is explained on the datasheet.

Doesn't sound a lot to me

We used the devices on military prototypes when I was just starting out.

Cheers

Mike T

Many thanks for that - now knowing its called a Coulometer makes finding information about it much easier. I will now be able to say for exactly how long my CD100 worked 40 years ago.

[Ed_Dinning]

Hi Geoff, these were often of Curtis instruments manufacture and the central bead moved against the scale to denote elaplsed time. They can be reversed to reset

Ed

[geoff1234]

Many thanks for that. In my CD100 the device is in series with a 750K resistor across the 5vdc line. What would the maximum hours on the scale be? My old brain cannot get its self around the mathmatics!

[Ed_Dinning]

Hi Geoff, max hours depends on composition of the Hg salts that are used in the tube .It is effectively a plating and depleting process at very low currents.
Note that these were developed to measure battery life on the lunar rover

Ed

[Cobaltblue]

Originally Posted by geoff1234

Many thanks for that. In my CD100 the device is in series with a 750K resistor across the 5vdc line. What would the maximum hours on the scale be? My old brain cannot get its self around the mathmatics!

It depends upon the supply voltage and the type of device I loosely based my assumptions on the devices linked to in post #7 and assumed a 5V supply.

The devices are rate in mA/H for FSD

The device that I related to was the 120PC with a rating of 4.167mA for 1HR FSD.

So assuming the supply to be 5V and no (significant) volt drop across the device I=V/R so ~ 6.67uA.


4.167mA/6.67uA =625Hrs

But there are a lot of assumptions here



The way to be sure would be to take it out of circuit (having taken pictures etc) Reverse the current on an external 5V supply and measure the time it takes to retun to zero.

You know what percentage of FSD it is currently so you could then calculate the FSD current.

Cheers

Mike T

[wave solder]

Another datasheet for the RS branded one here:-

https://assets.componentsense.com/im...6b8001a8fe.pdf

[Cobaltblue]

As 6.67uA would give 1000 hours with the device wave solder linked to thats a more likely match for the device being discussed here

Cheers

Mike T