A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

What do you mean by the sensor ?

Is it the actual photo pick up device or it is the sensor assembly is not
working ?

On Mon, Sep 3, 2018, 12:23 PM Mark Kahrs <mark.kahrs@...> wrote:

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

There are a number of sensor heads available for this instrument, I have
several of them here. They come in both 'imperial' and 'metric' units.

In terms of electronic components they only have a photo diode, a pot
and a fixed resistor in them.

In terms of optical components it's mostly just a filter and baffles to
collimate the incoming light I think.

The pot and resistor set the gain in the main instrument thus the
calibration is done in the sensor head.

We need to know which head and which bit is toasted to help much further!

Adrian


On 9/3/2018 8:23 PM, Mark Kahrs wrote:

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

J6511.

He says it's the sensor and I believe him. I suspect this may be made of
unobtanium.



On Mon, Sep 3, 2018 at 3:43 PM Adrian <Adrian@...> wrote:

There are a number of sensor heads available for this instrument, I have
several of them here. They come in both 'imperial' and 'metric' units.

In terms of electronic components they only have a photo diode, a pot
and a fixed resistor in them.

In terms of optical components it's mostly just a filter and baffles to
collimate the incoming light I think.

The pot and resistor set the gain in the main instrument thus the
calibration is done in the sensor head.

We need to know which head and which bit is toasted to help much further!

Adrian


On 9/3/2018 8:23 PM, Mark Kahrs wrote:

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

As I say, the gain is set in the sensor head so it's in the feedback
loop of the main instrument, I have a 6501 photopic head but don't have
the 6511 (cosine corrected) version. I'll be surprised if there isn't a
cal pot under a sticker somewhere. An iffy pot will also cause what he
sees (I've had that) but if it is the diode then there are things out
there that will work.

I've made a couple of slightly special (mechanically) heads which seem
to work fine using currently available diodes. He'll need to get a look
inside but most likely the diode is a TO5 wide bandwidth thing with a
separate filter to do the matching to the photopic curve with everything
behind a clever lens.

Adrian
On 9/3/2018 8:52 PM, Mark Kahrs wrote:

J6511.

He says it's the sensor and I believe him. I suspect this may be made of
unobtanium.



On Mon, Sep 3, 2018 at 3:43 PM Adrian <Adrian@...> wrote:

There are a number of sensor heads available for this instrument, I have
several of them here. They come in both 'imperial' and 'metric' units.

In terms of electronic components they only have a photo diode, a pot
and a fixed resistor in them.

In terms of optical components it's mostly just a filter and baffles to
collimate the incoming light I think.

The pot and resistor set the gain in the main instrument thus the
calibration is done in the sensor head.

We need to know which head and which bit is toasted to help much

further!

Adrian


On 9/3/2018 8:23 PM, Mark Kahrs wrote:

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

Hello Petru

I've put a couple of screenshots in the photos section (under TG501 5ns
2ns). The amplitude of the 5ns waveform is 1.24v pp and well within
spec. The 2ns is 0.9v pp. this appears below spec, but this is to be
expected on a 350 Mhz scope. I don't get a waveform on the 2456A for 1ns,
but this most likely due to the bandwidth limitation, rather than
indicating that the TG501 doesn't work on this range. I'll have to wait
until I have a working 1GHz scope before I can check this.

Regards

Kerry

Yes indeed, it's the aforementioned TO-5. What are your suggested
replacements?



On Mon, Sep 3, 2018 at 4:17 PM Adrian <Adrian@...> wrote:

As I say, the gain is set in the sensor head so it's in the feedback
loop of the main instrument, I have a 6501 photopic head but don't have
the 6511 (cosine corrected) version. I'll be surprised if there isn't a
cal pot under a sticker somewhere. An iffy pot will also cause what he
sees (I've had that) but if it is the diode then there are things out
there that will work.

I've made a couple of slightly special (mechanically) heads which seem
to work fine using currently available diodes. He'll need to get a look
inside but most likely the diode is a TO5 wide bandwidth thing with a
separate filter to do the matching to the photopic curve with everything
behind a clever lens.

Adrian
On 9/3/2018 8:52 PM, Mark Kahrs wrote:

J6511.

He says it's the sensor and I believe him. I suspect this may be made of
unobtanium.



On Mon, Sep 3, 2018 at 3:43 PM Adrian <Adrian@...> wrote:

There are a number of sensor heads available for this instrument, I have
several of them here. They come in both 'imperial' and 'metric' units.

In terms of electronic components they only have a photo diode, a pot
and a fixed resistor in them.

In terms of optical components it's mostly just a filter and baffles to
collimate the incoming light I think.

The pot and resistor set the gain in the main instrument thus the
calibration is done in the sensor head.

We need to know which head and which bit is toasted to help much

further!

Adrian


On 9/3/2018 8:23 PM, Mark Kahrs wrote:

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

Yes indeed, it's the aforementioned TO-5.  What are your suggested
replacements?



On Mon, Sep 3, 2018 at 4:17 PM Adrian <Adrian@...> wrote:

As I say, the gain is set in the sensor head so it's in the feedback
loop of the main instrument, I have a 6501 photopic head but don't have
the 6511 (cosine corrected) version. I'll be surprised if there isn't a
cal pot under a sticker somewhere. An iffy pot will also cause what he
sees (I've had that) but if it is the diode then there are things out
there that will work.

    I've made a couple of slightly special (mechanically) heads which seem
to work fine using currently available diodes. He'll need to get a look
inside but most likely the diode is a TO5 wide bandwidth thing with a
separate filter to do the matching to the photopic curve with everything
behind a clever lens.

Adrian
On 9/3/2018 8:52 PM, Mark Kahrs wrote:

J6511.

He says it's the sensor and I believe him.  I suspect this may be made of
unobtanium.



On Mon, Sep 3, 2018 at 3:43 PM Adrian <Adrian@...> wrote:

There are a number of sensor heads available for this instrument, I have
several of them here. They come in both 'imperial' and 'metric' units.

In terms of electronic components they only have a photo diode, a pot
and a fixed resistor in them.

In terms of optical components it's mostly just a filter and baffles to
collimate the incoming light I think.

The pot and resistor set the gain in the main instrument thus the
calibration is done in the sensor head.

We need to know which head and which bit is toasted to help much

further!

Adrian


On 9/3/2018 8:23 PM, Mark Kahrs wrote:

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?

Hi Folks,
   I just caught this thread because of the word "sensor" in the subject line - "photo-sensor" would have been more helpful, but I am glad I read the message, as it is a subject of interest (and it's come up from time to time as an off-topic conversation when we drift into debates about LEDs vs. incandescents!).
   I did not know that Tek made photo-optical sensors.   How common are these?   In particular, what do the PHOTOPIC sensors (i.e. those conforming to the CIE photopic curve, which is a modeled response of the average human eye to wavelength) go for on e-bay?  Can one even find the sensors?
   In direct response to Adrian, that Vishay sensor (BPW21R) won't work.  I have considered that one for light measurments.  Take a look at p. 3 of the datasheet here: https://www.vishay.com/docs/81519/bpw21r.pdf  At the bottom you see a comparison of the photo response of the Vishay photodiode to the CIE curve.   Those responses aren't even close.  I don't see how they can get away with calling that a CIE response.  Sure, at 550 nm, you can calibrate the sensor to give you close results with incandescent lighting.  But then consider a multi-spectral light source such as a white-light LED.  Typically they are driven by a UV or blue laser with a very strong peak somewhere around 450 nm.   The error there will be huge, and will seriously affect the accuracy of the measurement.
  I have an interest in verifying the "lumen output" claims of off-the-shelf, Chinese made LEDs for 110V lighting, so I poke around and search for sensors every once in a while.  I was very pleased to find this one, from TI:  http://www.ti.com/lit/ds/symlink/opt3001.pdf   Look at the response curve on p.1.   Now *THAT* is a photopic sensor!   The only problem is that it (and all its kin) have a digital (I2C) output.   Not having an analog output complicates things a bit.
  I suppose if it really needed to fit in the original Tek package, one could use an SOT-package Microchip processor to talk I2C to the TI sensor, pulse-width modulate the output and resistively divide down to mV to get something that mimics a photodiode, albeit ground-referenced and with an extra wire (for Vcc).  But it would have a photopic curve.
  But how accurate was the original Tek photopic response, AND what were the filters made out of?   If plastic, there's a chance they have drifted in color with age, and the response is no longer photopic....Ah.  Some of my questions are answered here:  https://www.atecorp.com/atecorp/media/pdfs/data-sheets/tektronix-j16_datasheet.pdf   So those Tek probes were pretty damned good.   Ok, now I want a J6523 (photopic, 1 degree acceptance angle), and a J6502-A (flat)!
 Dan
On Tuesday, September 4, 2018, 11:54:44 AM EDT, Adrian <Adrian@...> wrote:
If keeping the existing photopic filter (I'm assuming there is one) then
some research into the response of the current diode will be needed. I
think an alternative might be to remove the current filter  and use
either something like a Vishay BPW21R which has a filter built in and
may be accurate enough, or replace both with a matched diode/filter pair
from someone like Thorlabs but that can be pricey!


On 9/4/2018 1:11 AM, Mark Kahrs wrote:

Yes indeed, it's the aforementioned TO-5.  What are your suggested
replacements?



On Mon, Sep 3, 2018 at 4:17 PM Adrian <Adrian@...> wrote:

As I say, the gain is set in the sensor head so it's in the feedback
loop of the main instrument, I have a 6501 photopic head but don't have
the 6511 (cosine corrected) version. I'll be surprised if there isn't a
cal pot under a sticker somewhere. An iffy pot will also cause what he
sees (I've had that) but if it is the diode then there are things out
there that will work.

    I've made a couple of slightly special (mechanically) heads which seem
to work fine using currently available diodes. He'll need to get a look
inside but most likely the diode is a TO5 wide bandwidth thing with a
separate filter to do the matching to the photopic curve with everything
behind a clever lens.

Adrian
On 9/3/2018 8:52 PM, Mark Kahrs wrote:

J6511.

He says it's the sensor and I believe him.  I suspect this may be made of
unobtanium.



On Mon, Sep 3, 2018 at 3:43 PM Adrian <Adrian@...> wrote:

There are a number of sensor heads available for this instrument, I have
several of them here. They come in both 'imperial' and 'metric' units.

In terms of electronic components they only have a photo diode, a pot
and a fixed resistor in them.

In terms of optical components it's mostly just a filter and baffles to
collimate the incoming light I think.

The pot and resistor set the gain in the main instrument thus the
calibration is done in the sensor head.

We need to know which head and which bit is toasted to help much

further!

Adrian


On 9/3/2018 8:23 PM, Mark Kahrs wrote:

A friend acquired a J16 but the sensor is, in his words, "toast".

Any thoughts on replacing such a beast?