Recommendation for NI card to use as Power Supply of 5VDC, 1 to 20mA current range?

[ZohaibRamzane]

I have NI 9201 module to measure voltage across sensors. Amplifier circuit is already made to amplify voltage across the thermocouple.

For earlier question, i have to see.

[ZohaibRamzane]

I am looking for a programmable power supply that can be controlled within labview in constant voltage mode to provide fixed 5VDC and variable current in 1 to 20 mA range(controlled via labview)

Can someone recommend some affordable solution?

[cbutcher]

Let me ask some simpler questions:

1. I see you want to measure temperature with two different methods (RTD, thermocouple + amplifier). How much do you know about the readings you get from these, and the conversion to a temperature?
2. Are you familiar with Ohm's law?
3. Are you trying to quantify "self-heating" in the case of the RTD? How do you plan to do this?

Usually to make an RTD measurement, you use either:

• A fixed, known current value and a voltage measurement across the RTD (the voltage drop)
• A fixed, known resistor and two voltage measurements (across the RTD, and across the known resistor), and then this "ratiometric" measurement allows you to calculate the resistance of the RTD

In no circumstance that I can imagine (which isn't the same as no circumstance...) do you manage to have both a fixed voltage source, a controlled current value, and a resistor that varies only (significantly) with temperature. This system is overconstrained, probably impossibly so.

You could, if you wanted, have a fixed voltage drop and measure the current. Potentially you could use the communication with a power supply to "ask" it for the current (i.e. present) current (i.e. amperage) value when you make voltage measurements, but I expect this wouldn't be particularly accurate.

I notice also that I gained and lost a solution recently in this thread. That's a bit sad 😞

[GerdW]

Hi cbutcher,

---

@cbutcher wrote:
Potentially you could use the communication with a power supply to "ask" it for the current (i.e. present) current (i.e. amperage) value when you make voltage measurements, but I expect this wouldn't be particularly accurate.

---

SMUs tend to be quite accurate on voltage settings and current readings (or voltage readings for current settings)… (Accurate enough for Pt100 measurements.)

[cbutcher]

---

@GerdW wrote:

Hi cbutcher,

---

@cbutcher wrote:
Potentially you could use the communication with a power supply to "ask" it for the current (i.e. present) current (i.e. amperage) value when you make voltage measurements, but I expect this wouldn't be particularly accurate.

---

SMUs tend to be quite accurate on voltage settings and current readings (or voltage readings for current settings)… (Accurate enough for Pt100 measurements.)

---

Maybe I'm misunderstanding, or maybe I just have a power supply uniquely unsuited to this task (which would be fine, since I never considered using it for this task to make accurate measurements - just checks like "is it on? is it in CV mode?), but I'd have guessed something like the following:

V = 5V, R ~ 100 Ohms, => I ~ 0.05A.

My power supply will give me I think only to the nearest 10mA, so calling that +-5mA, I'm at +-10% uncertainty on my current value, leading to a similar error in resistance, no?

A Pt100 RTD at 100 Ohms is of course 0 deg C, and at 110 Ohms is around 26 deg C.

Perhaps it's more typical for a supply to give information down to the nearest mA, in which case you'd say only ~1% error, and perhaps 3 deg C? That's still large for me, but I suppose it depends on the measurement you're trying to make.

[GerdW]

Hi cbutcher,

I was mentioning SMUs like Keithley 2400. They can measure more accurately, but then you would source a small current and measure voltage...

[crossrulz]

---

@cbutcher wrote:

Maybe I'm misunderstanding, or maybe I just have a power supply uniquely unsuited to this task (which would be fine, since I never considered using it for this task to make accurate measurements - just checks like "is it on? is it in CV mode?), but I'd have guessed something like the following:

---

A Power Supply and a Source Measure Unit (SMU) are different things.  A power supply is really just geared to supply current to a circuit.  A SMU is designed specifically for measurements like PIV curves without the need for a separate DMM and power supply.  SMUs tend to not supply as much current, but you get much more accurate measurements.

[ZohaibRamzane]

I dont need SMU for measurement.  I have 9201 for voltage measurement.  I need a supply of 1 to 20mA range with 5VDC fixed ,controllable by LABVIEW. 

[GerdW]

Hi zohaib, 

you need an external power supply, providing 5V and capable of sourcing more than 20mA.

Then use a suitable resistor to create a voltage divider with your PT100...

[ZohaibRamzane]

Hi GerdW,

I have two things to clarify.

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.

Thanks.

Best Regards

Zohaib