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Help with LPM wiring db25 pinout PM5200 to attach Thermopile sensor

ducatidragon916

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Hello I was wondering if anyone could help me on a bit of information i was trying to obtain regarding the PM5200 Meter . now the main reason i would like to know or get the pinout of the Laser power head detector , is because i obtained a 200 Watt Thermopile sensor on ebay and want to hook this up to the Pm5200 meter. I am guessing the reason why they use a db25 pin connector is because of the possible connections to a board in the head which would possibly contain a preamp to condition the output power of the thermopile sensor so that the PM5200 can read more accurately and stably. I also think their might be a connection to a thermistor that would help to detect the ambient temperature and allow the meter to compensate for the surrounding temperature in diagnosing the accuracy of the detected output power of the laser beam. These are all conjectures on my part so I am stabbing in the dark. It also might just as simple as attach one side of the thermopile to this pin # and the other side of the thermopile to the ground pin # etc. Any information would be appreciated on this as I feel I have been spinning in a constant chase of the nose to the tail on the internet searches etc. At one point i considered just buy a laser detector head and plug it into this meter, however I have 2 of these thermopile sensors and was hoping to just machine some aluminum and attach the sensor to this and hook up the outputs to the meter. If i have to backward engineer a unit i would do this but it would be the last resort and would rather start on a fresh page . I am assuming the output of the thermopile is like 1mv/mw calibration reference etc. If you or anyone you might know that knows the pinout on what should be connected I would really appreciate it. Please advise....Thanks!!!!
 



ducatidragon916

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In addition I think that most of these professional systems use a voltage conditioning circuit inside the thermopile sensor head. This circuit most likely involves an Sensitive low voltage Op amp instrumentation level to amplify voltage less than 10mV range. I also think that there is a reference thermistor detection in the circuit to compensate for temperature difference in the cold zone to help keep the unit more accurate when measuring the power of a lasers beam. If i could get the pinout on the db25 connector it would allow one to figure which pins to apply the signal too and supply power to the circuit etc. Once this is identified i think one could assume the connection procedures. I am hopign someone can come up with this knowledge or provide a pinout diagram to help.
 

Encap

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Little if any chance anyone on LPF has direct knowledge of the pinout of your "antique" meter or any aspect --those were from late 1980's to early 1990's.

Have never heard of anyone on LPF having or speaking of one in past 10 years.

Maybe contact Coherent who bought Molectron in 2002 see: https://www.photonics.com/Articles/Coherent_Acquires_Molectron_Detector_Inc/a14569 --they might have available a service manual or user manual.

Call them and ask: https://www.coherent.com/measurement-control/main/laser-power-and-energy-meters

Only other choice is to contact LPM repair places and see if anyone is familiar with the Molectron PM5200
 
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ducatidragon916

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I have been busy re-engineering this meter and possible probe connection variations . I have discovered various aspects of this meter and the reading procedures of the head and what I should do in regards of using this meter and building a probe to connect to the db25 connector and use this meter. I believe this meter is quite sophisticated and is very advanced for what features it provides. When i finish the total research if anyone is interested I could provide the schematic and the photos i used to setup for use etc. I believe I am 80% done at this moment. I still in disbelief that nobody has any information on the hookup or the procedures for this unit since it was built in 1993 making the meter nearly 27 years old technology.
 

ducatidragon916

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I have that meter with a head, but no info on the pinout contacts.
Hey thats great!!!! I have been busy trying to backwards engineer the possible connections of the sensor etc. I know that there is a 8K eeprom in the db25 connecter shroud. I have some ideas of how it is connected but not 100%. Perhaps you can help out by cross referencing what i have in terms of the schematic and the way all of the components are connected etc. If you have some electronics background and are interested in helping out that would be great. I can provide the schematic thus far of what i have of how it is connected etc. The only thing is I have the bin data on the eeprom but have yet to decipher the contents and how it is setting up the meter. What is the power level of the sensor you have if you know it ?
Thanks for sharing !!!
 

Alaskan

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Hello, I have not used the meter for more than six months, packed away, will need to get it out and check. I have several thermopiles which can measure from 10 mw up to 5 KW. Have I needed the 5 KW head? Nope, but I'm ready!

Edit: I'm located near Saudi, assuming you are in the states my day is probably your night, answering posts may be on an opposite schedule than you are living.
 
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Alaskan

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My PM150 head the same:



That chip looks like an Op-amp to me, but of course many IC’s use that form factor. I cannot read any markings, they appear wiped. I work as an electronics tech/RF engineer, have a scope and DVM, if need be I can probe around to confirm what is going on. LPF member Lasersbee may recognize this circuit at first glance. Anyone else?

Probably much like this, see:

 
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ducatidragon916

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Oh wow thanks this helps alot for the visuals etc. How ever those leads are color coded and was wondering which leads connect to thermopile and i also assume that some of the leads are connected to a possible thermistor etc.. do you have access to taking photos of them head portion with the wires showing the color coding of where they go etc? Many thanks for what you have posted already etc...
 

ducatidragon916

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I noticed that the Sensor head is a coherent and not a molectron. I am assuming that it works fine with the meter etc. I think that it is essential about the color coding of the wires going to the sensor etc. Actually cant wait to see where the color coded wires are going to the thermopile and the possible connection to another sensor within the head such as a thermistor etc. with much anticipation on what you provide on bated breath....
 

Alaskan

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I will work on it. Coherent bought Molectron, same product.

Edit: instead of double posting, editing the info I found when opening the head here:

Black is common with one side of the thermopile
The other side of the thermopile is common with one side of a thermistor

I am having problems pinning this out due to the wiring of the thermistors and the two thermopile contacts. Can you possibly figure it out with this little information?



There are two tiny red magnet wires going to the thermopile sensor which appears to be some kind of resistive coil on the back side of it. I'm reluctant to open this head again with those tiny wires, too easy to break.
 
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Alaskan

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Here are some clearer zoomed in photo’s I took yesterday. You can see one thermistor is across the blue and green wire, one side of the other thermistor on the orange wire, the other side of that same thermistor probably on one side of the sensor. Click on them to see full size.





Even with my reading glasses I could not see this detail very well yesterday, only today after zooming in looking at photo's.

Edit:

I opened my 150 watt head and was able to take photo’s of both sides:

 
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Alaskan

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Photo's requested via PM:

Here are more photo’s, the test lead points to the side of the pot the orange wire goes to. In the third photo I am pointing the probe to the side of the pot I measured the lead on the other side to find less than 1 ohm resistance between that point and where the orange wire is soldered onto the PCB.


I didn't take a photo of the adjustment side of the pot straight on, couldn't see by eye what was written on it, but I believe I see 103 in the photo.

The orange wire goes to a thermistor, This wire measures 785 ohms to pin 1, and 797 ohms to pin 14,

The red wire goes to the other side of the same thermistor measuring one ohm to pin 1, 62 ohms to pin 14

The black wire has 62 ohms to pin 1 and one ohm to pin 14.

The blue wire has one ohm to pin 17.

Green has 1 ohm to pin 6.

The solder points on the small PCB are very difficult to get on, I need three hands. Do these numbers make sense? I tried to get this correct, even with great difficulty with the size of probes I have, I believe the above to be correct. If something does not make sense let me know and I will remeasure.
 
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