DAQ for EMG data acquisition - Page 1
Forum section: electronics / testgear

author: dritech
author_rank: Contributor
timestamp: October 17, 2017, 12:56:51 pm
content: Hi all,I am looking for a DAQ for monitoring EMG signals. The required specifications are the following:*At least 12CH ADC inputs*At least 5kHz sampling rate per channel*At least 14-bit ADCI was looking at USB-1616FS, but at $1,015 it is a bit too expensive.Can someone suggest any similar DAQ units which will work for this application.Also, can someone please explain the following terms/sentences used in the USB-1616FS datasheet:https://www.mccdaq.com/PDFs/specs/DS-USB-1616FS.PDF*with sample rates up to 50 kS/s per channel, continuous throughputs of 150 kS/s, and 32 kilosample bursts up to 200 kS/s*With hardware paced mode, the maximum throughput rate is 50 kS/s for one channel, or 9.5 kS/s per channel for all channels. With burst scan mode, the maximum throughput rate is 50 kS/s per channel for one, two, or three channels, and 16.5 kS/s per channel for all 16 channels.Am I right in saying 50kS/s is equivalent to 50kHz? What is the difference between paced mode and burst scan mode?Thanks in advance.

author: JPortici
author_rank: Super Contributor
timestamp: October 17, 2017, 01:34:48 pm
content: Quote from: dritech on October 17, 2017, 12:56:51 pmyes, saying 50 kS/s is equivalent to 50 KHz sample rate.have you checked out USB DAQs from National Instruments?http://www.ni.com/en-us/landing/low-cost-daq.htmlif you hit "configure" you get options with more channels:http://www.ni.com/en-us/shop/select/multifunction-io-device?modelId=124894

author: dritech
author_rank: Contributor
timestamp: October 17, 2017, 02:14:01 pm
content: Thanks JPortici.The datasheet of the USB-6211 does not state that the sampling rate is kS/s/ch.QuoteWhat would be the maximum sampling rate with this DAQ? will it be 250kS/s for all individual 16 channels?Also, the USB-6211 is not a simultaneous sampling DAQ (unlike the USB-1616FS). Will this somehow make any difference when monitoring and gathering EMG signals?

author: MasterT
author_rank: Frequent Contributor
timestamp: October 18, 2017, 12:39:36 am
content: I think, the data rate is limited by USB "bottle neck", regular PC may get 1-2 Mbits/sec over usb channel, dividing by 16-bits it boils down to 125 k sample per second. And after this limit, you have an option:a) stream 2-3 channels only with max sampling rate;b) store data in the memory buffer in burst mode from all 12-16 channels, than stop sampling and slowly transfer data to PC;c) decrease sampling rate down to < 10 ksps per channel.Arduino DUE (20$ on aliexpress) is able to sample 16 channels, it has one ADC 1 Msps, though capable to function as DAQ with 64 ksps for all 16 inputs. But problem with usb would be similar. If you are familiar with DSP, algorithm-math I mean, I 'd advise to delegate some raw processing to arduino itself, doing some kind of compression, than transfer pure data to PC in lower volume.

author: dritech
author_rank: Contributor
timestamp: October 18, 2017, 07:49:31 am
content: Thanks for your feedback.The specifications of the USB-6211 does not mention what is the maximum sampling rate for all channels. Infect, it states that the maximum sampling rate is 250kS/s (for multichannel). Is there something misleading, or am I interpreting the datasheet incorrectly?Datasheet:http://www.ni.com/pdf/manuals/375195c.pdfAlso, is the maximum speed of USB 2.0 1-2Mbits/sec? I was of the impression that it is much more than that.

author: rodpp
author_rank: Frequent Contributor
timestamp: October 18, 2017, 03:02:07 pm
content: I understand that the sum of the sample rates of all used channels must be limited to 250KS/s, probably because it uses one ADC to all channels.As your requirement is 5KS/s per channel and 12 channels, it is ok.Note that you will have 16 single ended channels or only 8 differential channels that provide a cleaner signal in many cases.It is a good idea to contact a NI representative and ask for assistance, maybe there is another board that suits better your requirements, like having 32 AI channels to use 16 differential if necessary.

author: Karel
author_rank: Super Contributor
timestamp: October 18, 2017, 04:03:50 pm
content: Quote from: dritech on October 17, 2017, 12:56:51 pmI don't see a specification for electrical isolation & patient safety. How are you going to deal with that?

author: nctnico
author_rank: Super Contributor
timestamp: October 18, 2017, 04:16:45 pm
content: I strongly recommend to get a DAQ which is designed for EMG use. This has the right safety precautions and standard connectors. One of the problems is that the signals need a lot more amplification than a standard DAQ will be able to do.

author: dritech
author_rank: Contributor
timestamp: October 18, 2017, 06:14:55 pm
content: Hi all,Something that I did not mention is that some of the signal conditioning (isolation, amplification etc)will be performd prior monitoring with the DAQ.@rodpp, the USB-1616FS one A/D converter per channel, but I am not sure about the NI USB-6211EDIT: The NI USB-6211 has one A/D for all 16 inputs.