Electrical interfacing of external PMT to ADC of FV300

[Shalin Mehta]

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Dear list,

We want to add external PMT to FV300 for having non-descanned path. We have old PMT from electron tubes (9798B with QL30 housing). We are a bit puzzled with its behaviour... will be great help if more experienced people could throw some 'light' :-)

We want to match the output of our PMT to ADCs of olympus so that we can interface the PMT using intermediate pre-amp circuit.
So we tested the PMT on the inverted confocal (Olympus FV300) by placing it right on top of the sample and blocking the laser by putting two filters before PMT window. We connected the signal connector (BNC) of the PMT housing to CRO (DC coupling 1 Meg impedance). We simultaneously compared the output of olympus PMT on CRO. The sample were fluorescent beads.

Now we observe this:
1. Output from olympus PMT+ pre-amp circuit was in range of 0-4 V when images appeared under and over saturated on fluoview software. So we concluded that olympus ADCs have a dynamic range of 0-4V.  Output of our PMT is negative voltage (as expected due to electrons flowing from anode to ground).
2. Our PMT does follow increase in fluorescence as sample is scanned at the same speed as olympus PMT (when we look at signals on CRO). But our PMT cannot follow the decrease in fluorescence!!

Our PMT outputs negative pulse and olympus PMT outputs positive pulse.  We see that our PMT 'peaks up' in negative direction exactly in same time as the olympus PMT. But on the opposite path the circuit is slow. To me it seems the problem is with way we are measuring output of PMT. Perhpas the thing is that current sees low time constant circuit when charging but long time constant circuit on the opposite path.

I could send the image and pics if someone thinks will help in making judgement.

could someone please comment on following questions?

1. I think PMT is a current source with internal capacitance and internal resistance connected in parallel. When we connect the CRO (1 Meg) to the housing we are putting a large resistance in parallel. Is that right to assume?

2. If above is the case, the current from sees low time constant path (low internal reistance (from cathode to anode to ground) times capacitance). But on the return path the internal resistance is high (I believe PMT is quite resistant to electron flow from anode to cathode). Since this leaves no return path with small time constant the circuit doesn't come to zero quickly.

3. Perhaps we can design a simple op-amp interving amplifier to provide isolation from CRO and match resistances correctly. If we have equivalent electrical circuit of the PMT we can do it quickly. Anyone has 'typical' internal resistance and capacitance values for QL30 housing? I searched Electron tubes website to no avail.

Any other thoughts on matching external PMT to the ADC of confocal?

As always, thanks for all the inputs,
Shalin



--
My co-ordinates:
Shalin Mehta, Graduate student
Graduate Programme in Bioengineering, NUS, Singapore
Email: shalin {dot} mehta {at} gmail {dot} com
Blog: <a href="http://electricsbm.blogspot.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)"> electricsbm.blogspot.com
Mobile: [phone]

[Guy Cox]

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

When Nuno Moreno and I did this on a Biorad MRC 1024, we

found we needed a little preamp to convert the negative, current

based signal to a positive voltage-based one.  Dino Sharma of

Biorad kindly gave us the necessary component so we didn't

have to build it.  May be either Dino or Nuno can add some

further details.

 

                                                                             Guy 

 

Optical Imaging Techniques in Cell Biology
by Guy Cox    CRC Press / Taylor & Francis

     http://www.guycox.com/optical.htm
______________________________________________
Associate Professor Guy Cox, MA, DPhil(Oxon)
Electron Microscope Unit, Madsen Building F09,
University of Sydney, NSW 2006
______________________________________________
Phone [phone]     Fax [phone]
Mobile [phone]
______________________________________________
http://www.guycox.net

---

From: Confocal Microscopy List on behalf of Shalin Mehta
Sent: Sat 6/10/2007 10:56 PM
To: [hidden email]
Subject: Electrical interfacing of external PMT to ADC of FV300

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Dear list,

We want to add external PMT to FV300 for having non-descanned path. We have old PMT from electron tubes (9798B with QL30 housing). We are a bit puzzled with its behaviour... will be great help if more experienced people could throw some 'light' :-)

We want to match the output of our PMT to ADCs of olympus so that we can interface the PMT using intermediate pre-amp circuit.
So we tested the PMT on the inverted confocal (Olympus FV300) by placing it right on top of the sample and blocking the laser by putting two filters before PMT window. We connected the signal connector (BNC) of the PMT housing to CRO (DC coupling 1 Meg impedance). We simultaneously compared the output of olympus PMT on CRO. The sample were fluorescent beads.

Now we observe this:
1. Output from olympus PMT+ pre-amp circuit was in range of 0-4 V when images appeared under and over saturated on fluoview software. So we concluded that olympus ADCs have a dynamic range of 0-4V.  Output of our PMT is negative voltage (as expected due to electrons flowing from anode to ground).
2. Our PMT does follow increase in fluorescence as sample is scanned at the same speed as olympus PMT (when we look at signals on CRO). But our PMT cannot follow the decrease in fluorescence!!

Our PMT outputs negative pulse and olympus PMT outputs positive pulse.  We see that our PMT 'peaks up' in negative direction exactly in same time as the olympus PMT. But on the opposite path the circuit is slow. To me it seems the problem is with way we are measuring output of PMT. Perhpas the thing is that current sees low time constant circuit when charging but long time constant circuit on the opposite path.

I could send the image and pics if someone thinks will help in making judgement.

could someone please comment on following questions?

1. I think PMT is a current source with internal capacitance and internal resistance connected in parallel. When we connect the CRO (1 Meg) to the housing we are putting a large resistance in parallel. Is that right to assume?

2. If above is the case, the current from sees low time constant path (low internal reistance (from cathode to anode to ground) times capacitance). But on the return path the internal resistance is high (I believe PMT is quite resistant to electron flow from anode to cathode). Since this leaves no return path with small time constant the circuit doesn't come to zero quickly.

3. Perhaps we can design a simple op-amp interving amplifier to provide isolation from CRO and match resistances correctly. If we have equivalent electrical circuit of the PMT we can do it quickly. Anyone has 'typical' internal resistance and capacitance values for QL30 housing? I searched Electron tubes website to no avail.

Any other thoughts on matching external PMT to the ADC of confocal?

As always, thanks for all the inputs,
Shalin



--
My co-ordinates:
Shalin Mehta, Graduate student
Graduate Programme in Bioengineering, NUS, Singapore
Email: shalin {dot} mehta {at} gmail {dot} com
Blog: electricsbm.blogspot.com
Mobile: [phone]

[Nuno Moreno]

Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

Yes,

at least the bio-rad 1024 used electrontubes pmts, model 9107. From what
I've seen on
http://www.photonics-solutions.com/ETI%20Data%20sheets/Photomultipliers/9798.pdf,
the pinout is the same. Hence, the easier solution would be to get a
bio-rad tail (which is just a pre-amp and black-level adjustment) and
connect the output to the olympus ADC directly.

You may try other solution for current to voltage amplification as long
as they are fast and low noise.

Regards,
NM



Guy Cox wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
> When Nuno Moreno and I did this on a Biorad MRC 1024, we
> found we needed a little preamp to convert the negative, current
> based signal to a positive voltage-based one.  Dino Sharma of
> Biorad kindly gave us the necessary component so we didn't
> have to build it.  May be either Dino or Nuno can add some
> further details.
>  
>                                                                              
> Guy
>  
> Optical Imaging Techniques in Cell Biology
> by Guy Cox    CRC Press / Taylor & Francis
>      http://www.guycox.com/optical.htm
> ______________________________________________
> Associate Professor Guy Cox, MA, DPhil(Oxon)
> Electron Microscope Unit, Madsen Building F09,
> University of Sydney, NSW 2006
> ______________________________________________
> Phone [phone]     Fax [phone]
> Mobile [phone]
> ______________________________________________
> http://www.guycox.net 
> <https://www.mcws.usyd.edu.au/exchweb/bin/redir.asp?URL=https://www.mcws.usyd.edu.au/exchweb/bin/redir.asp?URL=http://www.guycox.net>
>
> ------------------------------------------------------------------------
> *From:* Confocal Microscopy List on behalf of Shalin Mehta
> *Sent:* Sat 6/10/2007 10:56 PM
> *To:* [hidden email]
> *Subject:* Electrical interfacing of external PMT to ADC of FV300
>
> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Dear list,
>
> We want to add external PMT to FV300 for having non-descanned path. We
> have old PMT from electron tubes (9798B with QL30 housing). We are a bit
> puzzled with its behaviour... will be great help if more experienced
> people could throw some 'light' :-)
>
> We want to match the output of our PMT to ADCs of olympus so that we can
> interface the PMT using intermediate pre-amp circuit.
> So we tested the PMT on the inverted confocal (Olympus FV300) by placing
> it right on top of the sample and blocking the laser by putting two
> filters before PMT window. We connected the signal connector (BNC) of
> the PMT housing to CRO (DC coupling 1 Meg impedance). We simultaneously
> compared the output of olympus PMT on CRO. The sample were fluorescent
> beads.
>
> Now we observe this:
> 1. Output from olympus PMT+ pre-amp circuit was in range of 0-4 V when
> images appeared under and over saturated on fluoview software. So we
> concluded that olympus ADCs have a dynamic range of 0-4V.  Output of our
> PMT is negative voltage (as expected due to electrons flowing from anode
> to ground).
> 2. Our PMT does follow increase in fluorescence as sample is scanned at
> the same speed as olympus PMT (when we look at signals on CRO). But our
> PMT cannot follow the decrease in fluorescence!!
>
> Our PMT outputs negative pulse and olympus PMT outputs positive pulse.  
> We see that our PMT 'peaks up' in negative direction exactly in same
> time as the olympus PMT. But on the opposite path the circuit is slow.
> To me it seems the problem is with way we are measuring output of PMT.
> Perhpas the thing is that current sees low time constant circuit when
> charging but long time constant circuit on the opposite path.
>
> I could send the image and pics if someone thinks will help in making
> judgement.
>
> could someone please comment on following questions?
>
> 1. I think PMT is a current source with internal capacitance and
> internal resistance connected in parallel. When we connect the CRO (1
> Meg) to the housing we are putting a large resistance in parallel. Is
> that right to assume?
>
> 2. If above is the case, the current from sees low time constant path
> (low internal reistance (from cathode to anode to ground) times
> capacitance). But on the return path the internal resistance is high (I
> believe PMT is quite resistant to electron flow from anode to cathode).
> Since this leaves no return path with small time constant the circuit
> doesn't come to zero quickly.
>
> 3. Perhaps we can design a simple op-amp interving amplifier to provide
> isolation from CRO and match resistances correctly. If we have
> equivalent electrical circuit of the PMT we can do it quickly. Anyone
> has 'typical' internal resistance and capacitance values for QL30
> housing? I searched Electron tubes website to no avail.
>
> Any other thoughts on matching external PMT to the ADC of confocal?
>
> As always, thanks for all the inputs,
> Shalin
>
>
>
> --
> My co-ordinates:
> Shalin Mehta, Graduate student
> Graduate Programme in Bioengineering, NUS, Singapore
> Email: shalin {dot} mehta {at} gmail {dot} com
> Blog: electricsbm.blogspot.com <http://electricsbm.blogspot.com/>
> Mobile: [phone]

--
Nuno Moreno
Cell Imaging Unit
Instituto Gulbenkian de Ciência
http://uic.igc.gulbekian.pt
http://www.igc.gulbekian.pt
phone [phone]
fax   [phone]