Pneumatic controller regulates the load on a centrifugal freon compressor in a water cooling system, thus limiting the current input to an electric motor driving it. An electromechanical transducer monitoring the motor input current sends out air signals which indicate changes in the current to the pneumatic controller

Lovitt, T. F.

English

NASA Technical Reports Server

Adjustment 
Springs 
April 1966	 Brief 66-10160 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electropneumatic Transducer Automatically Limits Motor Current 
Power Input	 Power Air Supply 
50 Ps,
Current 
Transformer 
1500:5	 TRANSDUCER ASSEMBLY 
The problem: 
To provide a device for limiting current input to an 
electric motor to a predetermined maximum by auto-
matically adjusting the motor loading. A simple, 
efficient, and inexpensive method is required to limit 
the current input to an electric motor driving a centri-
fugal freon tompressor in a water cooling system. 
The solution: 
A pneumatic controller regulates the load on the 
compressor, thus limiting motor input current. The 
pneumatic controller receives an air signal by means of
an electromechanical transducer monitoring the motor 
input current. 
How it's done: 
The motor current controller consists of three sec-
tions, the motor/centrifugal compressor unit, the 
transducer assembly, and the pneumatic controller 
and associated linkage. The 1500:5 current trans-
former applies a current to the solenoid proportional 
to the input current of the motor. As the input current 
increases, the solenoid depresses the lever that causes 
a proportionate increase in the amount of air bled 
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AmIlk
	
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(continued overleaf) 
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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=19660000159 2020-03-11T17:31:08+00:00Z
from the 15-psi air supply line. Thus an increase in 
current causes a decrease in the air signal applied to 
the pneumatic controller. Adjusting the coarse and 
fine springs sets the current operating point. The air 
signal from the transducer assembly controls the 
pneumatically operated damper which in turn limits 
the flow in the suction side of the compressor. 
A rise in input current results in a drop in the air 
signal and causes the pneumatic controller to manipu-
late the butterfly valve to decrease the motor load. A 
decrease in input current produces a resulting increase 
in the motor load. Thus, the system provides an auto-
matic control of motor current by means of adjustable 
motor loading. 
Notes: 
I. In the particular application described, a thermo-
static control system was used in parallel with the 
current limiting device to provide temperature 
control. When the water temperature dropped 
below a specified minimum, the freon flow was re-
duced by means of a second signal applied to the 
pneumatic controller. Both control systems were 
connected to the pneumatic controller (in parallel) 
so that either could take precedence.
2. This controlling technique is simple and reliable 
and should be adaptable to systems other than 
compressor systems when the motor load is con-
trollable. 
3. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio, 44135 
Reference: B66-10160 
Patent status: 
No patent action is contemplated by NASA. 
Source: Thomas F. Lovitt 
(Lewis-253) 
Brief 66-10160	 Category 01


Electropneumatic transducer automatically limits motor current

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