programmable power Supply with labview for 5VDC,1-20mA current range

[GerdW]

Hi Zohaib,

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@ZohaibRamzane wrote:

1. Will NI 9265 meet my requirements(5VDC, 1-20mA)? If not, is there any other NI C series module?

2. If i use power supply for my requirement, for good setup, first i need to think which company's power supply is best and can be controlled through labview? 2nd i will use variable resistor with input sypply for better setup creation for students or any other good option if you can suggest because this experiment is to be performed by students in lab.

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1. No, it will not meet your requirements as has been written before!
   No, there is no such module from NI.
2. The brand of the power supply does not make a (huge) difference. You should take care of the type of power supply as cheap AC/DC converters might introduce a lot of (hig frequency) noise on their power output…
   I would even use a simple 7805 voltage regulator IC, supplied from the same 24V power supply (or similar) you use to drive the cRIO! (Place some capacitors before and after to stabilize the 5V line as suggested in the 78xx datasheets.)

[ZohaibRamzane]

Thanks for answering the questions. Still have some.

1. What is the reason of NI 9265 not meeting my requirements? Reason needed for discussion?

2. With 7805 VR, i cannot control current via labview. 

[cbutcher]

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@ZohaibRamzane wrote:

Thanks for answering the questions. Still have some.

1. What is the reason of NI 9265 not meeting my requirements? Reason needed for discussion?

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It cannot provide sufficient current without an external power supply. The datasheet shows how you should connect such a supply.

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@ZohaibRamzane wrote:

2. With 7805 VR, i cannot control current via labview. 

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If you have a resistor with a given resistance (set by e.g. temperature - an RTD) and you set the voltage drop (e.g. 5V) then the current is controlled by Ohms law.

Alternatively (and perhaps more commonly) you set the current, and measure the voltage. 

You cannot set both. This isn't an issue with LabVIEW or with hardware choice.

[ZohaibRamzane]

I have read the 9265 datasheet. Its written there(9V to 36VDC power supply required for input). This power can be supplied via compact RIO board 9024 that i am using. Then what is the problem?

"Alternatively (and perhaps more commonly) you set the current, and measure the voltage. 

You cannot set both. This isn't an issue with LabVIEW or with hardware choice."

To provide a labview interface for current control is part of my pre-thesis work. Therefore, it is mandatory for me.

[cbutcher]

Regarding the first part, you could probably parallel the power supply to the cRIO as the power supply for the module, but it will not provide it through the plug/socket that you use to connect the module to the chassis. 

Regarding the necessity - controlling current is no problem. The solution you want with the 9265 will happily allow LabVIEW to set a current (given a supply). But the voltage across a fixed resistor will obey Ohm's law.

Setting both the voltage and a varied current across a fixed resistor is not just difficult, or requiring of complicated programming. It is physically impossible.

So either:

1. Allow the voltage to vary in response to the changing (controlled) current

2. Allow the current to be fixed by the voltage level (no control of current except through the resistance)

3. Vary the resistance appropriately using some sort of PID loop and at least two digitally variable resistors (parallel and series). It's hard to believe this is a suitable solution to any system involving an RTD.

Almost certainly you want option 1, no? Then you can control the current arbitrarily and measure the resistance by measuring voltage. This allows conversion to temperature if you desire.

[ZohaibRamzane]

If i provide external power supply to NI9265,then it  will meet my requirement?

[GerdW]

Hi Zohaib,

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@ZohaibRamzane wrote:

If i provide external power supply to NI9265,then it  will meet my requirement?

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As long as your requirement is to control a current with a fixed 5V supply voltage: no. (As has been written several times before.)

Why don't you ask someone from Electronics department of your school/university? It seems you even miss the basics like Ohm's law…

[ZohaibRamzane]

Sorry for asking again and again

I now understood, the compliance voltage of NI 9265 is 12VDC if we draw 20mA current from it.

Thanks.

[ZohaibRamzane]

Dear NI experts,

I need to study the affect on temperature measurements of pt100, as i increase current passing through it. I have cRIO 9024 along with chassis. Also i have NI 9201 for voltage measurement across temperature sensor. I have searched the for NI module required for dc current range(0 to 20mA ). I found NI 9265 is suitable for this.

Before ordering this module, I need to confirm is this module meet my requirement(0 to 20mA DC current range controllable via Labview).

I asked this question earlier with voltage requirement but not this is not my requirement indeed. My requirement is to have current source as mentioned above.

Suggestion are welcome. Thank you all for support.

Best Regards

Zohaib

[GerdW]

Hi Zohaib,

why do you think it's a good idea to start a new thread for the very same topic?

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@ZohaibRamzane wrote:

Before ordering this module, I need to confirm is this module meet my requirement(0 to 20mA DC current range controllable via Labview). I asked this question earlier with voltage requirement but not this is not my requirement indeed. My requirement is to have current source as mentioned above.

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This 9265 is able to output 0-20mA. All you need is an external power supply as can be read in its datasheet…