DC Voltage and Current Measurements

[Redox_07]

Greetings LV Board,

Given:

NI 9215 4ch simultaneous +-10V DC Analog Input

NI 9203 8ch +-20mA DC Analog Input

NI cDAQ 9184 

Two DC Motors rated 0-180V (both), 1.8A and 5A respectively

Torque Transducer 0-5V DC output

Proximity Sensor 4-20mA DC output

Problem:

Measurement of Voltage and Current during various Operating points to determine various operating characteristics.

Suggested/ Failed Suggestions:

Resistive Voltage Divider with Zener and Paralleling resistors. 

Converters above the budget of the project.

Seeking Solutions:

1. Please recommend a cost-effective technique to measure Voltages ~200V with a resolution of at least 2V (To enable determination of Internal resistance of motor by applying armature voltage Va=2V at terminals and measuring small armature current Ia; R=2/Ia). This should match the input voltage range 0-10V of NI 9215.

2. Please recommend a suitable current measurement device/technique for measuring up to ~8A matching input current range of 0-20mA if NI 9203. My program will have sufficient run time for each operating point hence simultaneous channel current measurement may not be required (which I suppose is not available in NI9203??). 

3. I have a torque transducer giving voltage output range 0-5V suitable for NI9215 and an inductive proximity sensor giving current output range 4-20mA. I proposed to convert current measurement to voltage measurement by placing 250 Ohm parallel to current output lead and draw as voltage output (simultaneously with torque transducer on simultaneous channel measurement available in NI 9215 with BNC). However, the tolerance of resistance coming into play may negate the accuracy of my proximity sensor. As of now, I am using the proximity sensor only for RPM measurement. Do you think this is recommended? (As far as I discussed with my lab-mates a simple measurement of RPM shouldn't be affected because as each time the current output of proximity sensor dips detecting a metal, the voltage will also dip. here only the number of pulses in output waveform matter and not the precision.) Is this okay?

[GerdW · Accepted solution]

Hi Redox,

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@Redox_07 wrote:

Suggested/ Failed Suggestions:

Resistive Voltage Divider with Zener and Paralleling resistors. 

Converters above the budget of the project.

Seeking Solutions:

1. Please recommend a cost-effective technique to measure Voltages ~200V with a resolution of at least 2V (To enable determination of Internal resistance of motor by applying armature voltage Va=2V at terminals and measuring small armature current Ia; R=2/Ia). This should match the input voltage range 0-10V of NI 9215.

2. Please recommend a suitable current measurement device/technique for measuring up to ~8A matching input current range of 0-20mA if NI 9203. My program will have sufficient run time for each operating point hence simultaneous channel current measurement may not be required (which I suppose is not available in NI9203??). 

---

For 1 and 2 I suggest to spend some money on safety: use external signal converters!

For 3 using a simple resistor is ok as you only want to detect "dips"/pulses in a signal regardless of the actual voltage level. I see no need for <1% accuracy…

[Redox_07]

I just discovered following DAQ in my lab from concurrent project:

NI 9227 4ch 5Arms 24 bit Simultaneous Analog Input

NI 9225 3ch 300 Vrms 24 Bit Simultaneous Analog Input

I request the board to confirm whether I can use these to measure DC upto 5A and 200V respectively?

[Redox_07]

I just discovered following DAQ in my lab from concurrent project:

NI 9227 4ch 5Arms 24 bit Simultaneous Analog Input

NI 9225 3ch 300 Vrms 24 Bit Simultaneous Analog Input

I request the board to confirm whether I can use these to measure DC upto 5A and 200V respectively?

[GerdW · Accepted solution]

Hi Redox,

several options:

• read the spec sheet of those modules
• call your local NI tech support and ask them

No option:

• create a new thread just to ask the very same question again

IMHO your requirements will be satisfied by those modules.

I still suggest to contact someone responsible for (human/laboratory/electrical) safety measures for the planned setup: it seems you're not an electrical engineer.

[Redox_07]

Thanks GerdW for the solution and the advice. 

I posted as a new thread only anticipating that old threads do not get attention/immediate response.

I shall follow as advised. Thank you.