Fundamentals and Applications of Relays
Publication Date: 2012-Sep-15
The IP.com Prior Art Database
Page 01 of 26
FUNDAMENTALS AND APPL~EATIONS OF RELAYS
By J. C. Yang
Relays are various special devices with which certain special control funct£ons can he achieved, To tailor the instrumentation by using relays logically and properly is "must" required knowledge to a control engineer with little effort. Normally, a complicated and sophisticated control scheme can be realized by the use of several different types of relays. This paper will discuss the subject in =wo sections. First~ to explain the functions of several generally used relays, Second~ to show th~ techniques of their applications.
GENERAL DESCRIPTIONS OF RELAYS
The descriptions given belawwill be emphasized on the functions rather than the physical construction deta~is. The detailed constructions can be obtained from the manufacturers' caKalogs.
(A) Boo=ter Relays (See Block A)
They are normally used to reproduce pneumatic signals in a I:I ratio where the application requires amplifylng the volume of control air.
An example is a control valve located some distance from the controller.
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2 - Fundamentals and Appllcatinns o£ Relays
The booster relay with adjustable "bias" is to sh££t the signal range so as to get the best control value or shi£t the control range to another valve or device.
K ffi bias, adjustable
For example, a booster relay with '~ias" of +6 psi will shift the input signal of 3 ~ 15 psig to the output signal of 9 "~21 psig.
(B) Ratio Relays (See Block B)
These pneumatic relays are used to amplify or reduce control signals. For example, a 3 "~ 15 pslg control signal can he ampli- fied to operate a 6 ~ 30 psig final control element by using an amplifying relay (1:2 ratio); or the 3 ~15 psig signal can be "reduced to operate an 1 "~ 5 pslg final control element by using a reducing relay (3:1 ratio).
G= ~., ~--- ~uc~G ,e~LAY
R~,' AY I
Ratio relays with "bias" are used to change the •ontrol signals with different gain and bias.
For example, a direct action ratio relay with G = 2 and K =ii.5 w~ll shift the input signal of 3 "~ 9 pslg to the output signal of 3 ~-- 15 psig.
~cHf/'4/tTI6. D/AG,~AP'I ~
po =G(K- Pi)
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3 - Fundamentals and Appl£ca~£ons o~ Relays
(C) Reversin~ Relays (See Block C)
The relay is designed to deliver an output signal which decreases in direct proportion to an increase in input signal. A typical application is: where two control valves are operated by one con- troller - with the valves operatin~ in opposite directions as shown below:
Several different approaches can meet the system requirements. To use the reversing relay is one of them.
l~= ~IA$ ~ AMU~TA~L~
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4 - Fundamentals and Appllcatlons of Relays
(V) I. Low Selector (See Block D-l)
The relay will selec~ the lower of two inpu~ pneumatic signals, and ~ransmi~s the selected signal to ~he next element in the system.
.~H~FIA77~ DIAGRAP'I :
2. It$.gh Selector ~See Block D-2)
The relay w~ll select the...