protecting of PCI from high voltage

[Fahac]

Hi!

I am intending to use a NI PCI-6040E coupled with BNC-2110 connecter block by a SH 68-68 EP cabel to measure the output of a photodetector. I have just found that the photodetector output sometimes exceeds the input signal range of PCI card ( ~5 volt). I just measured it with voltmeter. Is there any one to help how can I protect of these hardwares? shall I use another hardware to control of input data? or is it possible to make a limitation by Labview software?

Thank you in advance,

Fa

[JÞB · Accepted solution]

the exact answer depends on what line you connect your photo detector to.  Theier is some input protection circutry on the device.  you want to stay within the limits you can read in the spec sheet

You can use external hardware to limit the voltage out of the photodetector.

There is no way whatsoever that any software can limit an external voltage source.

[johnsold]

Fa,

You cannot protect the physical hardware device by software. 

One way to provide protection is to use a series resistor and a Zener diode from the input connection to ground. Choose a diode voltage rating which is larger than your desired signal but smaller than the limit on the DAQ device. A 4.7 V rating for the Zener diode might work.  I do not know all the details of your signal to be able to make a more precise recommendation.

Lynn

[Fahac]

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@JÞB wrote:

the exact answer depends on what line you connect your photo detector to.  Theier is some input protection circutry on the device.  you want to stay within the limits you can read in the spec sheet

You can use external hardware to limit the voltage out of the photodetector.

There is no way whatsoever that any software can limit an external voltage source.

---

Hi!

Thank you for help. In fact I am a little confused with the different voltage ranges in the catalogues. I have found two different input ranges of (-+0.05 to -+10V, -2.5 to +2.5V) as an input signal range for NI 6040E.
And in that spec sheet that you have sent to me, Do you think it is safe for PCI card using of 0-25 Volt for AI <0..15>? Actually I am worry for DAQ stuff, for data measuring I can use a known filter.

Kind regards,

Faegheh

[Fahac]

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@johnsold wrote:

Fa,

You cannot protect the physical hardware device by software. 

One way to provide protection is to use a series resistor and a Zener diode from the input connection to ground. Choose a diode voltage rating which is larger than your desired signal but smaller than the limit on the DAQ device. A 4.7 V rating for the Zener diode might work.  I do not know all the details of your signal to be able to make a more precise recommendation.

Lynn

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Hi johnsold,

I really thank you. I think it should work. I will look for a electronical engineer in our department. Do you think is it easy to make? and can I make it compatible with BNC connector?

Best regards,

Faegheh

[johnsold]

Faegheh,

First, regarding the questions about ranges: The device has programmable amplification so the various ranges from +/-0.05 V to +/- 10 V refer to the voltages which will give full scale inputs to the A/D converter at various Gain (or Range) settings. The circuits also have limits above which damage may occur.  For your device that limit is +/-11 V from ground at any input.

Consider this example. Set the range to +/- 1 V. If the input is 0.6 V everything works fine. If the input is 1.3 V, the value returned by the DAQ Read may be approximately 1 V or you may get an error. If the voltage is 12 V, the device could be damaged, you might or might not get an error, and you might or might not get a reading, but if you do get a reading it will certainly not represent the input voltage.

Next, regarding the Zener diode circuit. If you only are concerned about protecting the device from damage, then select a Zener rated at 10-11 V. If you want to keep the readings from saturating, then the Zener voltage need to be lower than the Range setting but higher than the maximum voltage or the desired signal. If the voltage can be positive or negative, then you will need two zeners or a diode bridge plus a Zener. 

This is a very simple circuit to make once you select the appropriate device. One easy way to connect it in a BNC connector situation is to put a BNC male and a BNC female connector on a small box with the resistor and Zener diode inside the box. I think Pomona makes small boxes that work very well for that. If you do not mind the crude appearance and do not need shielding, you can use flange connectors with long screws between the flanges.

Lynn

[Fahac]

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@johnsold wrote:

Faegheh,

First, regarding the questions about ranges: The device has programmable amplification so the various ranges from +/-0.05 V to +/- 10 V refer to the voltages which will give full scale inputs to the A/D converter at various Gain (or Range) settings. The circuits also have limits above which damage may occur.  For your device that limit is +/-11 V from ground at any input.

Consider this example. Set the range to +/- 1 V. If the input is 0.6 V everything works fine. If the input is 1.3 V, the value returned by the DAQ Read may be approximately 1 V or you may get an error. If the voltage is 12 V, the device could be damaged, you might or might not get an error, and you might or might not get a reading, but if you do get a reading it will certainly not represent the input voltage.

Next, regarding the Zener diode circuit. If you only are concerned about protecting the device from damage, then select a Zener rated at 10-11 V. If you want to keep the readings from saturating, then the Zener voltage need to be lower than the Range setting but higher than the maximum voltage or the desired signal. If the voltage can be positive or negative, then you will need two zeners or a diode bridge plus a Zener. 

This is a very simple circuit to make once you select the appropriate device. One easy way to connect it in a BNC connector situation is to put a BNC male and a BNC female connector on a small box with the resistor and Zener diode inside the box. I think Pomona makes small boxes that work very well for that. If you do not mind the crude appearance and do not need shielding, you can use flange connectors with long screws between the flanges.

Lynn

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 Lynn,

I am thinking about the Zener to see how to make it. Thank you for help. In fact, my first and the most considering is to protect the device, because even in normal situation the signal somtimes exceeds from +/- 10 V and it is not predictable. I am thinking to use a Zener rated ~ 10 V. In case of saturation of the signal I can use a optical density filter in front of the photodetector.

I also have another question, The voltage in my measurement can be positive or negative, it is a quadrant photodiode, and give a subtract of voltage in two different sides, connected to a dual channel power supply and already has a ground. my question is could I use this ground for DAQ stuff? or how can I define a ground for BNC 2110 or PCI 6040 in case of ground-referenced source (gs)? Shall I just connect the body of computer to the power supply ground?

Kind regards,

Faegheh