View Full Version : Humidity Chamber and Optotrack Measurements

Darrell Goertzen
05-06-1997, 11:42 PM
Greetings to everyone,

I have a two part question.

PART 1: We are planning to buy or make a humidity chamber for material
testing with a MTS or Instron test machine. We need a temperature controlled
and humidity controlled test environment. The chamber would be approx. a 500
mm cube with a supply of high humidity air at a temperature of 37C.

We have information from MTS regarding their temperature controlled water
bath and also spray nozzles to create a high humidity condition. The
humidity supply is not under closed-loop control and the standard chamber
size (250mm diameter cylinder) is not a suitable size.

Does anyone have experience (or comments) regarding buying, making and/or
using a humidity and temperature controlled test chamber. Are small scale
commercial ones available or have people made their own (if at all)?

PART 2. We will be using an Optotrack 3020 (active infrared markers)
to record rigid body motion during testing in the above mentioned chamber.
Therefore, a clear plastic? glass? barrier will be between the camera and
the markers. We have not yet done a calibration check under these conditions
and anticipate some kind of effect due to this barrier.

The only similiar reference I have found is a paper by Lam et al.,
(Calibration Characteristics of a Video Dimension
Analyser (VDA) System, J Biomech 25(10):1227-1231 1992) which assessed the
calibration of a 2D visible light measurement system with a 6.4mm thick,
low-refractive index glass between the camera and specimen. They found
changes in the calibration parameters with the glass and also by varying the
angle of incidence.

I would be happy to hear from anyone with experience using an Optotrack (or
other active infrared system) with a clear sheet between the cameras and
markers, or thoughts about distortion of 3D measurements, best type of
material, etc.

I will post a summary of responses.

Thanks for your help.

Darrell Goertzen

M.E. M|ller Institute for Biomechanics
University of Bern
Murtenstrasse 35, P.O.Box 30
CH-3010 Bern

Tel: +41 (0)31 632 4976
Fax: +41 (0)31 632 4951
Email: goertzen@mem.unibe.ch
http:// cranium.unibe.ch