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Fundamentals and Applications of Relays

IP.com Disclosure Number: IPCOM000221686D
Publication Date: 2012-Sep-15

Publishing Venue

The IP.com Prior Art Database

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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.

~Locl< ,~



Page 02 of 26

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

BLOC/< ~

Ratio relays with "bias" are used to change the •ontrol signals with different gain and bias.

Direct action

Reverse action

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 ~

SuPpLy

po =G(K- Pi)



Page 03 of 26

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~



Page 04 of 26

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...