calling electronics gurus for help

[badger1666]

many thanks jerry , that saves trying to correct it from outside the head
off to search pl to find that pic and see if it shows which pot to adjust

thanks again most helpfull

[dera236]

Hi all

Have Just purchased a OPHIR 20C power head, and i have a few questions regarding them!

Does any one know what the output is like on these I.e. what is the mV output range.
Does the signal swing +/- W.R.T 0V?
Does the signal in the quiescent state with no laser light entering the device sit at zero or is there an offset?
What is the maximum swing in mV when a 0-5W laser is projected into the device?
If anyone can shed light on any of the above no pun intended it would be most useful as I would like to scale the output to give say 1V = 1W
Having access to a few real life figure will allow me to design up the electronics to achieve this.

Regards

K

[badger1666]

Why would you need to design anything to read it
I use a 5 digit MV meter from virtual village ,a +-12v dc-dc converter from rs, 6 rechargeable aa's and a plastic box
From maplin , job done reads to 20w with a 1mw resolution

[lasersbee]

Actually you would need addition cooling of the head over while
inputting over 5Watts of Laser Power.

The output of those OPHIR 20c heads is already calibrated by
OPHIR to 1mV=1mW...

Jerry

[Things]

1. 1mV=1mW
2. Yes, it can swing into the -'s, which you need to be careful of if you're using it with a microcontroller as they can get fussy with - voltages.
3. It will vary, most power meters have a zeroing potentiometer or button to offset it before a measurement.
4. 5W = 5000mW, so 5000mV or 5V if it's zero'd first.

It is easy to use them up to 5W with a simple microcontroller as their power:voltage ratio is fairly high. You can use an external voltage reference on a microcontroller to effectively adjust your resolution. Many ATMega controllers have an internal 1.1Vref, which is what the Kenometers used for the sub 1W range to give a bit more precision.

[lasersbee]

There is the problem again... The Kenometer uses a 10Bit on board ADC
that at 5000mW will have a resolution of 5000/1024=4.88 mW.

You would get a closer 1mW resolution using one of these at ~$23.00..

http://www.ebay.ca/itm/180537737481?...84.m1438.l2649


Jerry

[Things]

Yes, my point was, using different vrefs, you can effectively adjust the resolution of your meter, like the 1.1V internal vref of the ATMegas 1100/1024 = 1.07mW resolution.

Obviously a better ADC is the best option.

[dera236]

Actually you would need addition cooling of the head over while
inputting over 5Watts of Laser Power.

The output of those OPHIR 20c heads is already calibrated by
OPHIR to 1mV=1mW...

Jerry

Thanks for the message jerry,
Still feel that it would be well worth adding a launch resistor the buffering the output voltage with an op amp to protect the head electronics for inadvertent shorting. Believe me when i say it happens.
Had a 100kW system at work with a lead connected to an un-bufferd signal, the signal terminated at a Tektronik DPO. Normally fine but someone had been fiddling and the scope was left term to 50 ohms instead of 1meg. result system failed to operate and it took an incompetent field service guy 8 day's before I turned up and found the issue in ten minuets.