Synchronize the 2701 beginning scan with 2260B test sequence

[DieLiz]

Hi Craig,

I need to let the sequence run and scan the channels with a timestamp of the measurement.

I have two sequences to run.

• The first sequence: current limited to ~2A and the voltage is set at 20V for the first ~15sec; then the current stays at~2A and the voltage drops to ~8V for ~60sec, then it shuts down. With this sequence I'll scan the channels at max speed (every ~0.0113sec).
• The second sequence: It cycles a 'resistor' on-off for 10 times. I do not know the exact sequence yet, but every cycle it takes about 30 to 45 minutes. The sequence will be at least 5hours. For this sequence I plan to use the whole buffer of the 2701 (buffer should be 450000 data points max) which it means that I'll scan the channels every ~0.04sec max.

Yesterday I've merged the two VIs into one, I'm not sure if it's the best practice and I'm open suggestions. The new VI is attached below. To synchronize the beginning of the scan with the beginning of the sequence I used a 'flat sequence' and it seems ok. As you mention, the delay between the two instrument is variable. If I can not eliminate the delay I'm ok with it but I would like to be able to quantify it, so that I can quickly clean the data before the beginning of the sequence.

Let me know if I gave you enough info for understanding the project.

Thank you so much for your help and your time.   

[cstorey]

Now that I see the entire thread I have more questions and I'm skeptical that providing code would help you achieve anything.  (beyond learning how to synch the two instruments.) 

Are you truly measuring a resistor?  What kind of resistor is this?  What material, what resistance and what capacitance and inductance.  Ideal resistor has 0 capacitance and 0 inductance.  All resistors have some parasitics, good one its very negligible.  What do you expect to see?  Why are you testing with this equipment?  

Voltage across any good resistor will settle fast.  You might get ringing (overshoot/undershoot) when the voltage is applied but the timescale to observe that won't be captured by this DMM, you would need a scope to capture or a very fast DMM. I do this in some tests where a 30V 200ns pulse is applied to <50Ohm load and I measure voltage across a small shunt resistor in series.  Voltage settles in 20-50ns.  If I match the load to 50Ohms, just like the supply output then its <10ns. 

Now for the longer measurement how will you distinguish drift in voltage over time due to supply and not the resistor?   Will you be maintaining the resistor temperature exactly to account for heating or changing physical properties (changes R) with time?  Organic resistors or thin films might have enough C/L to see some effects, possibly with this test setup, but they would have to be poor resistors to see effects on 11ms time scale measurement resolution.

What you really want for a resistor test is an SMU - source measure unit.  You can source voltage and measure current at the same time.  You can account for losses in cabling by using a 4pt Kelvin connection.  You probably want to read through this to see exactly the best setup - https://www.tek.com/document/handbook/low-level-measurements-handbook

Now if you still want to try to code it..

Craig

[DieLiz]

Greg, thank you for sending me the LowLevelHandbook link. I had time to read through the 1^st section and the 3^th one, I had no idea this is such a huge topic and I’m glad you pointed it out. I’ll keep reading and learning how to take V and A measurements and improve my method. In the meantime I need to complete the code for testing our parts. We have been doing this manually and my effort is for automating this task with LabVIEW, make it repeatable, increase accuracy and make it fast for the operators. Below I answered a few questions I believe I can disclose with you.

What kind of resistor is this? It is a heater made of metals alloy wire.

What material? The heaters are made of mostly tungsten wire. Based on their uses they have different, shapes, diameters and lengths. The measured resistances are on the order of .5Ω to 5Ω. I never thought to measure capacitance and inductance, for my purposes I can neglect them for now but I’ll consider them in the future for improving accuracy.

What do you expect to see? I expect to see how fast they can warm up (limiting the current, and the voltage) and which temperature they reach. I also need to test them with on-off cycles (warm-up, stabilize at xxxx°C for xxxx sec or mins, cool down completely and repeat).

Why are you testing with this equipment?  This is what I have to work with. It worked (semi-manually) so far. Now I’m trying to write a LV code to make it easy, fast, and repeatable.

How will you distinguish drift in voltage over time due to supply and not the resistor? IDK. I’m reading the book you sent me to better understand the how to take measurements of A,V. For now I’m only aware that the resistance of the heater changes with temperature.

I hope these info will help to understand my LV code goals and i'm open to any suggestions.

Thank you so much.

Diego 

[DieLiz]

Hi guys, 

When I run PSupplyDmmSyncro.vi with Test On-Off 5-29-2020 5 cycles 2hrs.txt test sequence, the vi gets stuck and never end. Does anyone have any suggestion for what is wrong and how to fix it? I've tried to create a test sequence with shorter steps of about 60sec (and repeat them multiple times when necessary) but it still gets stuck into infinite loops. 

Thank you for your time, your help is much appreciated!

Diego