View Full Version : Summary of Data Logger Responses

Frank Buczek Phd
07-14-1998, 06:34 AM
Dear Colleagues,

This message includes a summary of responses to a question I posted in May,
regarding data logging devices for pressure measurements. Thank you to all
who responded.

Frank L Buczek, Jr, PhD
Director, Motion Analysis Laboratory
Shriners Hospitals for Children
1645 West 8th Street, Erie, PA 16505, USA
(814) 875-8805 voice, (814) 875-8756 facsimile
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Design specifications and pricing for Pressure Sensing Transducers and
associated data recording device.
-- commercially available preferred
-- custom fabrication considered

We want to assess compliance for the use of a plastic body jacket in the
treatment of scoliosis; recommended usage will be 23 hours ON, 1 hour OFF,
with exceptions from time to time.

-- Pressure sensing will be needed only for on/off states, rather than the
measurement of actual pressure values.

-- Pressure sensors should NOT be adversely affected by temperature (i.e.,
an instrumented body jacket left in a hot automobile should not record wear
compliance during this time period.)

-- Two pressure sensors are anticipated, mounted flush with the interior
surface of the body jacket, most likely adjacent to the lateral rib cage on
each side of the body.

-- The data recorder should be of low profile (less than 3/8 inches), and
preferably of flexible or somewhat concave construction. It should be
capable of sampling the sensors once each hour, and storing the information
for a six month duration, although other sampling rates and durations will
be considered. The power requirements for the device should be met with an
integral power supply, such that the entire data recorder and power supply
are no larger than 6 in x 4 in x 3/8 in. The smaller, the better.

-- The sensors and data recorder will be fabricated into a body jacket by
an orthotist.

-- The recorder should be capable of downloading to an IBM compatible
personal computer; we expect this to occur once every six months (see

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RESPONSES (Edited for brevity by FB)

Have you considered using force sensing resistors (FSR)? A FSR is an
electronic element whose resistance varies with the pressure applied to the
element. It is a 0.3 mm thick laminated polymer construct. They come in
various sizes and are distributed by Interlink electronics, California,
(805) 484-1331 , fax (805) 484-8989.

Kenton R. Kaufman, Ph.D., P.E.
Associate Professor of Bioengineering
Co-Director, Biomechanics Laboratory
128 Guggenheim
Mayo Clinic
200 First Street SW
Rochester, MN 55905
Phone: (507) 284-2262
FAX: (507) 284-5392
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Try and call Dr. Avanish Patwardan. He can be reached either at Loyola
School of Medicine, IL. or at the Rehabilitation Research And
Development Center, VA Hines Hospital, Hines IL.

He has done considerable work developing sensors to do similar things.

Ted Morris tmorris@med.umn.edu
Senior Project Engineer V: 612-626-2561
MVS/Prosolvia F: 612-626-0679
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We sell tactile pressure transducers. Check out our site at
to see if this is what you are seeking.

Jeffrey Stark
Sensor Products Inc.
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Saw your post and thought I'd pass on some ideas. If you're looking for a
very reliable and relatively inexpensive data logger that is quite small
and virtually indestructible, you should check out the HOBO and Tattletale
by Onset computer.

I used these for an ambulatory monitor about 8 years ago, and found them
excellent, easy to program, and quite reliable. .....Temperature stability
is a concern for the contact sensors. I've used
Force Sensing Resistors (FSR, Interlink) for years for footswitches, and
they are reasonably reliable, but I don't have any experience with them in
a chronic application. What you might want to do instead is use an
infrared proximity sensor that would trigger when the body jacket is worn
and so the body is in close contact with the plastic. I'd use at least 2
sensing sites, probably 3, to reduce the chance that they could be

Interlink is at: http://www.interlinkelec.com/

IR Proximity sensors: http://www.turck.com/PROX.HTM

James Carollo, Ph.D., P.E.
Senior Research Scientist
Mobility Research and Assessment Laboratory
The University of Texas
Southwestern Medical Center at Dallas
9705 Harry Hines Blvd., Suite 105
Dallas, TX USA 75208 (214) 351-2041
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We do have a product which may be of interest to you. The recorder will
accept one or two sensors in the size of a matchbox recording at 50 Hz for
hours. A notebook computer will be required for reading the data and the
calibration file......

Susan Diekrager
Executive Vice President
novel electronics inc.
964 Grand Avenue
St. Paul, MN 55105
tel. 612.221.0505
fax 612.221.0404
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I am an electrical engineer working at the institute of
Biomedical Engineering at the University of New Brunswick, and
have considerable experience in such instrumentation tasks.

One of our particular research projects involved the monitoring of
EMG, foot load and knee angle bending during normal working
activities of nurses. ...The fabricated system collected data for up to 4
and then downloaded the information to a PC computer via a standard
RS232 link.

For your application, we could borrow the foot sensing circuitry
developed for the "nurse" study and the data download
software. However, to extend the data collection period to 6
months and drop the sampling rate, a re-design of the
processor section of our instrumentation would be necessary. As
absolute pressure information is not required this would be
relatively simple as no analog-to-digital converter would be
required. My concept at this stage is that every hour a
micro-power timer would "wake up" the processor, which would take
look at the force sensors to see if the subject was wearing the cast
and store the result (YES or NO) in non-volatile memory. This memory could
approximately 16000 YES/NO decisions. If you sample at 30 minute
intervals this translates into approximately 330 days.

Dennis F. Lovely.
Research Professor Tel: (506) 453 4966
Institute of Biomedical Engineering Fax: (506) 453 4827
University of New Brunswick Internet: LOVELY@unb.ca
NB, E3B 5A3
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