Metabolic analyzer determines a patient's walking or ambulation speed and simultaneously measures his metabolic parameters. Analyzer is designed to move at some preselected human ambulation speed. During test, patient is connected to system and follows analyzer closely while his metabolic data is being monitored

Currie, J. R.

English

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V 
V0 = V•(VV) 
V  
April 1974	 1	 B73-10480 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Pseudotachometer for Mobile Metabolic Analyzer 
A new mobile metabolic analyzer has been developed 
which determines a patient's walking or ambulation 
speed and simultaneously measures his metabolic param-
eters. The analyzer is designed to move at some pre-
selected human ambulation speed. During a test, a 
patient is connected to the system and follows the 
analyzer closely while his metabolic data is being 
monitored. 
Basically, the system comprises an electrical cart, or 
pseudotachometer, supporting a metabolic analyzer. 
The cart is designed to travel over a tape track laid out 
over a prescribed course. As shown in the illustration, 
the cart has passed a left turn and is moving toward a 
right turn. The paths shown represent the velocities
VR, VL, and VM of the right and left rear wheels and of 
the patient, respectively. In this case, the patient is 
walking to the right of the right rear wheel. 
The development of the pseudotachometer is based 
on the following analysis: As shown in the figure, the 
distances X and Y are constants, while 0 and r are 
unknowns, and the patient's velocity is to be computed. 
Using the left turn as reference (see figure) constant 
angular velocity 0 1 may be expressed by 
• VL VR	 "M (1) 
r 1 r 1 +X r1+X+Y 
. 
• 
Operational 
Amplifier
Configuration for Pseudotachometer Signal When 
the Patient is Positioned to the Right of the Cart
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000480 2020-03-17T07:31:36+00:00Z
By equating the first two expressions on the right-hand 
side of this equation, r 1
 may be expressed as follows:
Equation 4 is valid only if the patient is walking to 
the right of the right rear wheel. Should the patient be 
walking between the two rear wheels, a different 
relationship may be obtained using a similar analysis, 
where r l = -  
VR.VL	
(2) 
Now, solving the last two expressions on the right-hand 
side of equation 1 for r, reduces r 1 to 
(X+Y)VL 
r1=  
VM-VL	
(3) 
Hence, a substitution for r 1 from equation 3 into 
equation 4 reduces the solution for VM to 
Y 
VM = V - (VL.VR) (4) 
where all the terms on the right-hand side are either 
known or can be measured. The same development 
holds for the right-hand turn. Equation 4 also holds for 
movement-along the straight segment. 
Based on equation 4, a pseudotachometer is built 
using a single operational amplifier with corresponding 
input-output characteristics (see figure). The velocities 
of the cart wheels are determined by voltages equivalent 
to VL and VR derived from tachometers installed on the 
left and right rear wheels, respectively. The resistor ratio, 
R2 /R 1 , then is adjusted to match the distance ratio, 
Y/X. The output voltage of the amplifier then determines 
ambulating velocity VM.
VM = VR+ R2 (VL-VR)	 (5) R1+ 2 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10480 
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS.PAT 
Marshall Space Flight Center, Alabama 35812 
Source: J. R. Currie
Marshall Space Flight Center

(MFS.22909) . 
B73-10480	 Category 05,02


Pseudotachometer for mobile metabolic analyzer

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