PSN-L Message - Subject: Update -- USB Data Acquisition

I spent a little more time with the Futek A/D. I also took its cover = off to look inside. First my observations on performance -- I think my first impressions of extremely high noise are due to a bug = in their software. When I look at only one channel at a time I get = results much closer to what I would expect from a chip of this type = i.e.. about 50 counts p-p noise with the input shorted (100 ohms ) When both inputs are active the result is over 2000 counts noise but = the display does not look right. The distribution is not at all uniform = over all possible values. In fact it doesn't even make sense. I think = the hardware is probably good to ~18 bits p-p or 22 bits RMS which is = what the chip spec says it should be .=20 The included software --as it is --is not good. But some of the files = could be useful for development of custom software. Inside the box -- The chip is a TI MSC1200Y2. The chip includes 4 channel 24 bit A/D and = a 8051 microprocessor with extensive IO. The USB interface is the usual = FTDI serial to USB device. All unused pins on the MSC1200 are readily = accessible and there is a header inside which is probably for loading = the program. If one has the interest and skills the board could be an excellent = stating point for a nice system since there is quite a bit of processing = power inside and access to all of the IO of the processor. The only = difference between the 4 channel device and the two channel is only two = channels of the input components are populated and the firmware only = calls two channels . The board itself and all active parts appear to be = the same. Conclusion ---=20 A good starting point but the product ,as is, has some problems. The = hardware itself has a lot of flexibility and a convenient package for = low bucks but it would be a real project to make something of it. On the = other hand it might be worth some effort. I intend to make a few more tests -- if anything comes from them I will = report on it . If you have a suggestion for a test or would like to try = it yourself just let me know. Dave Nelson=20 Rolling Hills Estates, California=20 From: ian=20 Sent: Wednesday, January 05, 2011 11:28 AM To: psnlist@................. Subject: Re: Fw: USB Data Acquisition if you want a usb daq, then have a look at = http://sine.ni.com/nips/cds/view/p/lang/en/nid/201987 I haven't used = usb versions but I know their products are very good. I use a pci = version for my system. Some software comes with the device but I don't = know if it would do all that is needed for a station. =20 You also get them on ebay. cheers Ian On 04/01/2011 23:53, Dave Nelson wrote:=20 =20 I saw this A/D on Ebay and decided to try it . I bought the two = channel version for $99. =20 I tested it using the included software with the inputs terminated in = 100 ohms. The result was EXTREMELY POOR !!!!=20 The noise level is ~2000 counts peak to peak apparently independent = of the sample rate. This results in an effective resolution of closer = to 12 bits not 24 on a p-p basis .=20 This is not too surprising based on the specs for the low cost = delta-sigma A/D chips.=20 The software makes and displays a record from the start time to the = end time.=20 The time resolution of the real time display gets worse as the record = length gets longer. It is not a scope type display with a variable time = interval. So far I have come to the conclusion this thing is useless with its = included software. There are .dll files for windows if one could write = new or adapt existing software for display/analysis but that may not = improve the noise. The apparent independence of the noise as the sample rate is varied = leads me to the initial conclusion that the A/D is running at a fixed = high sample rate and the lower effective sample rates are derived by = pure decimation.=20 I need to take a closer look at it but so far I am totally unimpressed = and don't recommend this device for any useful purpose. 24 bit A/D's in general do not perform as well as one would expect or = hope . Read the effective resolution specs very carefully and note that = they usually refer to RMS noise whereas the noise we want to use for = seismic records is most likely peak to peak. The difference is 3 to 4 = bits.=20 We are not in the audio business where RMS noise may be more = appropriate. Frequently the effective resolution is not much better than = 16 bits at 200 sps. Larry clearly understand the importance of the noise and goes to great = lengths to reduce it in his A/D boards. Sometimes the very expensive = 24 bit A/Ds are not nearly as good as the manufacturers lead one to = believe. =20 Save your money on this one. Dave Nelson=20 Rolling Hills Estates , California =20 Do any of you have any experience with these ACD devices. They appear = to compete with DataQ products. =20 http://www.futekinst.com/futek/dataacquisitionsystem.asp =20

I spent a little more time with the = Futek=20 A/D. I also took its cover off to look inside.

First my observations on performance=20 --

I think my first impressions of = extremely high=20 noise are due to a bug in their software. When I look at only one = channel=20 at a time I get results much closer to what I would expect from a = chip of=20 this type i.e.. about 50 counts p-p noise with the input shorted (100 = ohms=20 )

When both inputs are active the result = is over 2000=20 counts noise but the display does not look right. The = distribution is=20 not at all uniform over all possible values. In fact it doesn't even = make sense.=20 I think the hardware is probably good to ~18 bits p-p or 22 bits RMS = which is=20 what the chip spec says it should be .

The included software --as it is --is = not good. But=20 some of the files could be useful for development of custom=20 software.

Inside the box --

The chip is a TI MSC1200Y2. The = chip includes=20 4 channel 24 bit A/D and a 8051 = microprocessor=20 with extensive IO. The USB interface is the usual FTDI serial to USB=20 device. All unused pins on the MSC1200 are readily accessible and = there is=20 a header inside which is probably for loading the program.

If one has the interest and skills the = board could=20 be an excellent stating point for a nice system since there is quite a = bit of=20 processing power inside and access to all of the IO of the processor. = The only=20 difference between the 4 channel device and the two channel is only two = channels=20 of the input components are populated and the firmware only calls two = channels .=20 The board itself and all active parts appear to be the=20 same.

Conclusion ---

A good starting point but the product = ,as is, has=20 some problems. The hardware itself has a lot of flexibility and a = convenient=20 package for low bucks but it would be a real project to make = something of=20 it. On the other hand it might be worth some effort.

I intend to make a few more tests -- if = anything=20 comes from them I will report on it . If you have a suggestion for a = test or=20 would like to try it yourself just let me know.

Dave Nelson

Rolling Hills Estates, California =

From: ian

Sent: Wednesday, January 05, 2011 11:28 AM

To: psnlist@..............

Subject: Re: Fw: USB Data Acquisition

if you want a usb daq, then have a look at http://sin= e.ni.com/nips/cds/view/p/lang/en/nid/201987 =20 I haven't used usb versions but I know their products are very = good. I use=20 a pci version for my system. Some software comes with the device = but I=20 don't know if it would do all that is needed for a station. =

You=20 also get them on ebay.

cheers

Ian

On 04/01/2011 = 23:53, Dave=20 Nelson wrote:=20

I saw this A/D on Ebay and decided to = try it . I=20 bought the two channel version for $99.

I tested it using the included = software with the=20 inputs terminated in 100 ohms. The result was EXTREMELY POOR=20 !!!!

The noise level is ~2000 counts = peak to=20 peak apparently independent of the sample rate. This results in an = effective=20 resolution of closer to 12 bits not 24 on a p-p basis . =

This is not too surprising based on = the specs for=20 the low cost delta-sigma A/D chips.

The software makes and displays = a record=20 from the start time to the end time.

The time resolution of the real time = display gets=20 worse as the record length gets longer. It is not a scope type display = with a=20 variable time interval.

So far I have come to the = conclusion this=20 thing  is useless with its included software. There are .dll = files=20 for windows if one could write new or adapt existing = software for=20 display/analysis but that may not improve the = noise.

The apparent independence of the = noise as the=20 sample rate is varied leads me to the initial conclusion that the A/D = is=20 running at a fixed high sample rate and the lower effective sample = rates are=20 derived by pure decimation. =

I need to take a closer look at it = but so far I=20 am totally unimpressed and don't recommend this device for any useful=20 purpose.

24 bit A/D's in general do not = perform as well as=20 one would expect or hope . Read the effective resolution specs very = carefully=20 and note that they usually refer to RMS noise whereas the=20 noise we want to use for seismic records is most likely peak to=20 peak. The difference is 3 to 4 bits.

We are not in the audio = business where RMS=20 noise may be more appropriate. Frequently the effective = resolution=20 is not much better than 16 bits at 200 sps.

Larry clearly understand the = importance of the=20 noise and goes to great lengths to reduce it in his A/D = boards.  =20 Sometimes the very expensive 24 bit A/Ds are not nearly as good = as the=20 manufacturers lead one to believe.

Save your   money on = this=20 one.

Dave Nelson

Rolling Hills Estates , California=20

Do any of you have any experience with these ACD devices. = They =20 appear to compete with DataQ products.

http://www.futekinst.com/futek/dataacquisitionsy= stem.asp

These=20 device appear to compete with DataQ with 16 or 24 bit offering.=20

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