http://confocal-microscopy-list.275.s1.nabble.com/Electrical-interfacing-of-external-PMT-to-ADC-of-FV300-tp590482p590484.html
at least the bio-rad 1024 used electrontubes pmts, model 9107. From what
the pinout is the same. Hence, the easier solution would be to get a
> 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 +61 2 9351 3176 Fax +61 2 9351 7682
> Mobile 0413 281 861
> ______________________________________________
>
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: +65 90694182