Electromechanical flowmeter remotely and accurately monitors the flow rate and total volume of a transparent liquid discharged from a dispensing system. A dual dispensing tube system provides a relative reference level which permits compensation for temperature variations

Grant, D. J.

English

NASA Technical Reports Server

September 1965
	 Brief 65-10273 
NASA TECH M I UN 4^]AA 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical information, Springfield, Virginia, 22151. 
Electromechanical Flowmeter Accurately Monitors Fluid Flow 
Volume Volume 
Readout I	 I  Readout 
Pulse	 PulseFlow Rate	 Flow Rate	 Pulse	 Pulse 
Counter	 DiR.	 Readout	 Readout	 Diff.	 Counter 
Pulse Pressure Pulse 
Gen. Source 
II
Gen. 
Lead 
Photoelectric 
Detector
- Amplifier 
And 
Voltage 
Servo Comparator
] Feedback
Meniscus
ull l Indicator 
Reference I	 (	 ) Reference 
Voltage 
_j Voltage 
Control 
Drive	 Mech. I	 •-::f: . Mech. Drive Control	 Drive J Drive Control Liquid Out
The problem: Providing an instrument that will 
remotely and accurately monitor the flow rate and 
total volume of a transparent liquid being discharged 
from a dispensing system. One approach for contin-
uous flow indication is through the use of a photo-
electric detector and light source that are mechanically 
driven along a transparent dispensing tube to track or 
follow the displacement of the liquid meniscus. 
Previous instruments based on this approach do not 
give an accurate indication of the total amount of 
liquid dispensed since they depend upon an inherently
inaccurate reference point that cannot be set from a 
remote location. These instruments do not compen-
sate for temperature variations which expand or con-
tract the liquid and thus alter the level of the meniscus 
in the dispensing tube. 
The solution: An electromechanical flowmeter 
employing two similar dispensing tubes and two 
photoelectric detectors that are accurately driven on 
lead screws to track the meniscus in each tube. A null 
indicator connected to the outputs of the detectors 
(continued overleaf) 
MEW
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19650000271 2020-03-11T17:19:36+00:00Z
fixes the level of the liquid in one tube as a reference 
with respect to the level of the liquid in the other 
tube. Compensation for any temperature variations is 
maintained by alternately referencing between the two 
tubes as the liquids are dispensed. 
How it's done: A gas pressure source and two 
remotely controlled valves connected to each of the 
dispensing tubes are used to regulate the flow of 
liquid from the system. The photoelectric detectors 
are positioned for parallel longitudinal movement 
along the dispensing tubes to sense the position of 
each meniscus. Signals from the detectors are coupled 
to a conventional amplifier and voltage comparator 
circuit which in turn is connected to a null indicator. 
This indicator registers a null or minimum reading 
only when the voltage levels of the signals from the 
two detectors are approximately equal and thus 
establishes the position of the meniscus in one of 
the tubes as a reference for the meniscus in the 
second tube. 
As liquid is dispensed, each detector independently 
tracks the displacement of the meniscus in the tube 
with which it is associated. The detector outputs and 
reference voltages (equal to the output voltages from 
the respective detectors) are fed to the remote drive 
controls which regulate the variable-speed motors that 
drive the detectors along the lead screws. For each 
of the dispensing tubes, the electrical output line 
from the detector, the drive control, the mechanical 
drive, and the lead screw constitute a feedback 
circuit which automatically positions the detector in 
accordance with the position of the meniscus of the 
liquid in the corresponding tube. The pulse generators, 
coupled to each lead screw, generate a predetermined 
number of pulses for each revolutiOn of the lead screw. 
The pulse counters and readouts, by means of multi-
plication circuitry not shown, give the volume of 
liquid dispensed. Liquid flow rates are obtained by 
connecting the pulse counters to pulse differentiators 
and additional readouts.
Notes: 
I. Since the entire operation may be controlled from 
a remote station, this flowmeter should be 
particularly useful for accurately monitoring the 
flow of small quantities of hazardous (radioactive 
toxic, or explosive) liquids, or liquids that must 
be dispensed in closed chambers, such as vacuum 
chambers. 
2. The same principle of operation may be used with 
more than two dispensing tubes. 
3. Instead of using the dual dispensing tube system 
to provide a relative level reference between the 
liquids in each tube, the same principle can be 
applied to one or more tubes by connecting an 
independent reference voltage source to the 
amplifier and voltage comparator. 
4. If the dispensing tube or liquid is opaque, magnetic 
detectors may be used instead of the photoelectric 
detectors. In this case, a buoyant slug containing 
magnetic material will have to be placed on the 
liquid surface in the tube. 
5. Inquiries concerning this innovation may be 
directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland, 20771 
Reference: B65-10273 
Patent status: NASA encourages the immediate 
commercial use of this invention. It is owned by 
NASA, and a patent application has been filed. When 
patented, royalty-free nonexclusive licenses for its 
commercial use will be available. Inquiries concerning 
license rights should be made to NASA, Code AGP, 
Washington, D.C., 20546.
Source: Daniel J. Grant 
(GSFC-357) 
Brief 65-10273	 Category No. 01


Electromechanical flowmeter accurately monitors fluid flow

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server