Photodiode to DAQ

[pooh1]

Dear folks,

I am trying to measure light intensity using a photodiode (Thorlabs, SM1PD1B). I have PCI-6251 DAQ and BNC-2090A and SCB-68 accesory.

I am trying to connect my bare Si photodiode (Thorlabs, SM1PD1B) to SCB-68 Channel 7 and read a voltage response. 

I wired a photodiode cathode to terminal 57 and an anode to terminal 23 as DIFF mode and also place 100kohm resistor between photodiode anode and termial 23 as discribed in following link.

http://forums.ni.com/ni/board/message?board.id=250&message.id=13207

I also tried to put 100kohm resistor b/w A23 and AIGND and wire a photodiode to AI7 and AI15. But it did not work.

Sombody suggested to use a circuit from Thorlabs (attached). I think, I can wire this circuit to my photodiode. But I wonder how I can get a voltage source? Can I use DAQ (5V voltage source) voltage source to apply a voltage to photodiode? Then, How?

 I want to use this channel to check a laser signal change during my sample measurements. I have an Thorslab amplifier for another photodioe for my real measurement and can get the voltage signal w/o a problem. But I don't want to buy or build a transimpedence amplifer for this channel. I am not good at this. If I can get any reasonalbe signal from this photodiode w/o an amplifier, I am ok with it. Do anybody know how I can get a voltage signal (0 to 10V or 5V) from this photodiode without an amplifier? Do i really need an amplifer for this measurement???

Thanks in advance. 

[KateB]

Hi pooh1,

You cannot measure anything previously, because you've not give any bias to a diode.

Connecting to a circuit as shown in its specification is a good idea.

6251 supply can pay up to 1A max.

Therefore, you can try using it, but remember that the circuit of photo diode use negative supply.

Since then, you need to swap between ground and +5V.

For AI, you should use diferential mode, but I don't think you need external resistor to ground.

Regrads, Kate

[pooh1]

Thanks for the reply! Kate.

More questions......:(

I have SCB-68. Which terminal do I have to use for power supply from DAQ? Can I use, for example, terminal 14 (+5V) and terminal 24 (AI GND)? I am not sure where I can get +5V and GND from my SCB-68 Board.

Another question is you mean that I don't need 1kohm resistor in the circuit? Do I still need 0.1 uF condensor? load resistror 50 ohm would be enough? What voltage range will I get from my photodiode??

Thanks in advance

Young-

[AnalogKid2DigitalMan]

To calculate approvimate Voltage out, use Vo = P * Rlambda * Rl.

Where  P is indident power on detector in Watts
 Rlamdba is the responsitivity in Amps/Watt (see the graph in the datasheet)
 Rl is your load resistance in ohms.

Example: 10mW at 700nm with a 50 ohm load resistor
Vo = 0.010W * .5A/W * 50 ohms = 0.25V

Look in the manuals for your DAQ card and SCB-68 to determine where to obtain 5V, typically at the 5V and GND pins.

-AK2DM