Data Sheet for Product

Technical Instructions RL 243 A Commercial Duty Analog Relay
Document Number 155-107P25
Rev. 1, April, 2000
Page 2
Siemens Building Technologies, Inc.
Applications
The analog relay can be pneumatically piped in a variety of different combinations. Each
combination represents a relay application that can be used to perform a specific
function in a control loop. These applications are listed in
Table 1
and described in
Figures 2 through 15
beginning on page 3.
Table 1. Analog Relay Applications.
ReIay Application Figure
Ratio 1 in = 2 out 2
Ratio 2 in = 1 out 3
Summing or Adjustable Advancing 4
Averaging 5
Differential Pressure 6
Highest Pressure Signal Selector
or
Adjustable Minimum Pressure
7
Reverse Acting 8
Minimum Pressure with Characterized Output 9
Characterized Minimum Pressure 10
Direct Acting 11
Direct Acting with Positive Positioning Override 12
Lowest Pressure Signal Selector 13
Signal Inverting 14
Signal Retard 15
Operation
The relay output pressure at port R is dependent on the interaction of pressures at the T,
TD, and TR ports and on the availability of an air supply at port S. See
Figure 1
. The
basic relay formula is as follows:
TD + (T - TR) = R
Where:
R is the output signal port.
T is a direct acting input port.
TD is a direct acting input port.
TR is a reverse acting input port
S is the air supply port.
NOTE:
R cannot be greater than S, and (T – TR) cannot be less than 0 psig.
The T pressure is exerted downward against the top of the T diaphragm and is opposed
by the TR pressure pushing up against the bottom of the TR diaphragm. When T is
greater than TR, the difference in force (T – TR) is transmitted by the stem downward
against the TD diaphragm assembly. When TR is greater than T, the net downward force
is zero.
The other force acting downward is the TD pressure against the top of the TD
diaphragm. These downward forces are balanced by R port pressure pushing up against
the bottom of the R diaphragm. The R port pressure is determined by the net forces
acting on the TD and R diaphragm assembly that positions the supply and exhaust
valves.
Discontinued