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what is my sampling time if I take 1 sample per channel
Angelantoni
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06-06-2005 03:10 AM
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Hi
I have 6280 m series DAQ card, and scxi 1125 signal conditioner, am reading thermocouple voltages via the signal conditioner using 1328 terminal blocks. If i read 1 sample per channel, considering there are 512 channels to read. what would be my sampling rate? is there any way i can set this? am reading the values from thermocouple for every 2 seconds. at what sample rate should read so that settling time does not come in to picture. my gain in scxi module is 50 with max and min values +0.1v and -,0.1v respectively.
Thanx a lot
Arun
I have 6280 m series DAQ card, and scxi 1125 signal conditioner, am reading thermocouple voltages via the signal conditioner using 1328 terminal blocks. If i read 1 sample per channel, considering there are 512 channels to read. what would be my sampling rate? is there any way i can set this? am reading the values from thermocouple for every 2 seconds. at what sample rate should read so that settling time does not come in to picture. my gain in scxi module is 50 with max and min values +0.1v and -,0.1v respectively.
Thanx a lot
Arun
06-06-2005 03:45 AM
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hi again
If i use DAQmx timing vi to set the sampling frequency to about 1000 samples per seconds, then i belive settling time shd not be problem for me, is it? does the DAQ card automatically allow the voltage to settle and then sample the voltage?
Thanx in advance
Arun
If i use DAQmx timing vi to set the sampling frequency to about 1000 samples per seconds, then i belive settling time shd not be problem for me, is it? does the DAQ card automatically allow the voltage to settle and then sample the voltage?
Thanx in advance
Arun
Marni
NI Employee (retired)
06-07-2005 02:11 PM
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Hello Arun.
Thank you for contacting National Instruments. If you want 1 sample per channel every 2 seconds, set DAQmx timing to continuous with Sample Rate set to .5 (sample every 2 seconds). Then on the DAQmx Read set Samples to Read to 1 (1 sample every time). There is an example in the Example Finder that you can modify to do what you want. Go to the Help Menu and select Find Examples. Browse Hardware Input and Output>>DAQmx>>Analog Measurements>>Voltage for Cont Acq&Graph Voltage-Int Clk.vi. To see the points you collect right click on the data output of the DAQmx Read and Create Indicator. Expand the array and you will see the points for 152 samples. Also, you might want to replace the graph with a chart. Please let me know if you have any questions. Have a great day!
Marni S.
National Instruments
Thank you for contacting National Instruments. If you want 1 sample per channel every 2 seconds, set DAQmx timing to continuous with Sample Rate set to .5 (sample every 2 seconds). Then on the DAQmx Read set Samples to Read to 1 (1 sample every time). There is an example in the Example Finder that you can modify to do what you want. Go to the Help Menu and select Find Examples. Browse Hardware Input and Output>>DAQmx>>Analog Measurements>>Voltage for Cont Acq&Graph Voltage-Int Clk.vi. To see the points you collect right click on the data output of the DAQmx Read and Create Indicator. Expand the array and you will see the points for 152 samples. Also, you might want to replace the graph with a chart. Please let me know if you have any questions. Have a great day!
Marni S.
National Instruments
06-08-2005 03:22 AM
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hi Marni
Thanx for your reply. I have few more questions, i dont understand the meaning of sampling rate is it time between first sample and second sample? or time between sampling all the signals. I belive it should be the first one, another question is if i set the max and min val of a signal in channel property, a gain is applied to the siganl my DAQmx, and every time i want to acquire a channel this gain is first applied and then the signal is sent to ADC were it is sampled, now how do i ensure that the sample is taken only after the signal is setteled and not when the signal is oscillating, I belive if i reduce the sampling rate between signals then sample is taken after the signal has settled, is this correct? if yes please tell me how exactly this is done.
And also I have 500 channels, 1 sample per channel will come to 500 samples, so 500 samples every 2 second meaning sample rate of 250 samples per second. is his OK?
Thanx in advance
Arun
Thanx for your reply. I have few more questions, i dont understand the meaning of sampling rate is it time between first sample and second sample? or time between sampling all the signals. I belive it should be the first one, another question is if i set the max and min val of a signal in channel property, a gain is applied to the siganl my DAQmx, and every time i want to acquire a channel this gain is first applied and then the signal is sent to ADC were it is sampled, now how do i ensure that the sample is taken only after the signal is setteled and not when the signal is oscillating, I belive if i reduce the sampling rate between signals then sample is taken after the signal has settled, is this correct? if yes please tell me how exactly this is done.
And also I have 500 channels, 1 sample per channel will come to 500 samples, so 500 samples every 2 second meaning sample rate of 250 samples per second. is his OK?
Thanx in advance
Arun
Marni
NI Employee (retired)
06-09-2005 10:38 AM
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Hello Arun.
The Sample Rate is how many samples you collect per channel per second. So in your case, you want to take one sample every 2 seconds on every channel so the sample rate is 1 sample/ 2 seconds = .5 samples. The way the task is set up, you don't need to take the 500 channels into account.
You are correct when you say a smaller sampling rate between signals makes sure that the samples are taken after the signal has settled. However, the interchannel delay is so small for the PCI 6280, that for multiple channels you can have a sample rate up to 500kS/s. Please let me know if you have any questions. Have a great day!
Marni S.
National Instruments
The Sample Rate is how many samples you collect per channel per second. So in your case, you want to take one sample every 2 seconds on every channel so the sample rate is 1 sample/ 2 seconds = .5 samples. The way the task is set up, you don't need to take the 500 channels into account.
You are correct when you say a smaller sampling rate between signals makes sure that the samples are taken after the signal has settled. However, the interchannel delay is so small for the PCI 6280, that for multiple channels you can have a sample rate up to 500kS/s. Please let me know if you have any questions. Have a great day!
Marni S.
National Instruments
