POWERS® Controls
Technical Instructions
Document No. 155-042P25
RL 243-6
September 10, 2018
RL 243 MP Multi-Purpose Relay
Siemens Industry, Inc.
Description
The Powers RL 243 MP Multi-Purpose Relay is a pneumatic auxiliary device designed to
provide a variety of pneumatic control functions for the typical control system.
Applications include direct and reverse acting amplifying, signal advancing, minimum
pressure relay, and lower pressure transfer. (See Figures 2 through 10.)
The relay operates on a force balance principal and is provided with a Powers two-valve
design to assure stability and prevent unnecessary air consumption. Internal relief
assembly prevents signal lock-up and assures fail-safe operation. The relay housing is
provided with integral brackets to facilitate installation without a separate bracket.
A single spring adjustment is provided to allow setting the relay for desired operation.
The relay is adaptable for flush panel mounting to facilitate manual readjustment if
desired.
Product Number
243-0009
Operation
The relay output pressure at port R is dependent upon the adjustable setting of spring
S1, the interaction of pneumatic signals at ports TD and TR, and the availability of a
supply source at port S. The basic relay formula can be expressed as follows:
R = (TD + (S1 - TR) = S
NOTE: (S1 - TR) cannot be less than zero,
Where:
R is the output pressure
TD is a direct acting input variable
S1 is the setting of the adjustment spring
TR is a reverse acting input variable (opposing S1)
Technical Instructions RL 243 MP Multi-Purpose Relay
Document Number 155-042P25
September 10, 2018
Page 2 Siemens Industry, Inc.
Operation,
continued
Figure 1.
The return line pressure R depends on the force exerted by adjustment spring S1 and air
pressures at TD and TR. TR pressure is exerted against the bottom of the upper
diaphragm, opposing S1. However, if S1 is greater than force TR, this difference (S1
minus TR) is transmitted by the stem to the main diaphragm below. The other force
acting downward on the main diaphragm is caused by the air pressure at TD. These
downward forces are balanced by air pressure R pushing up on the main diaphragm.
Spring force S1 is adjustable up to an equivalent pressure of 25 psi.
Specifications
Instrument air supply
Normal 0-2 5 psi (0 to 172 kPa)
Maximum 30 psi (207 kPa)
Temperature limits
Ambient 40 to 120°F (4.4 to 49°C)
Storage -20 to 120°F (-29 to 49°C)
Adjustments Spring S1 0 to 25 psi (0 to 172 kPa)
Hysteresis Within 0.25 psi (1.7 kPa)
Relief valve differential Within 1.0 psi (6.89 kPa)
Accessories
Panel mounting For flush mounting,
with adjustable knob, dial
plate and mounting bracket
Surface bracket For exposed surface mounting
(Use with Panel Mounting Kit above)
RL 243 MP Multi-Purpose Relay Technical Instructions
Document Number 155-042P25
September 10, 2018
Siemens Industry, Inc. Page 3
Application
The multi-purpose relay is factory calibrated with a 15 psi spring adjustment for reverse
acting service. However, the multi-purpose relay provides a number of specific control
actions which are frequently utilized in control systems. Some of the typical applications
where this relay can be applied are as follows. Additional applications can be obtained
depending upon how it is piped and applied with other devices in a single system.
• Direct acting amplifying (See Figure 2).
• Reverse acting amplifying (See Figure 3).
• Lower pressure transfer relay (See Figure 4).
• Signal advancing relay (See Figure 5).
• Minimum pressure relay (See Figure 6).
• DA or RA limit control (See Figures 7 and 8).
• Signal inverting relay (See Figure 9).
• Characterized minimum pressure relay (See Figure 10).
Direct Acting (DA)
Amplifying Relay
Output pressure will vary directly with input pressure. Relay is fail-safe and cannot
generate an output signal unless a source of air is available at S-port (Figure 2).
Figure 2. Direct Acting (DA) Amplifying Relay.
Technical Instructions RL 243 MP Multi-Purpose Relay
Document Number 155-042P25
September 10, 2018
Page 4 Siemens Industry, Inc.
Reverse Acting (RA)
Amplifying Relay
A rise in input pressure will cause an equivalent fall in output pressure. Initial maximum
relay output is adjusted with spring setting. Relay is fail-safe and cannot generate an
output signal unless a source of air is available at S-port (Figure 3).
Figure 3. Reverse Acting (RA) Amplifying Relay.
Lower Pressure
Transfer Relay
Output pressure will equal the lower of the two input signals. Internal relief valve prevents
signal lock up when pressure at S-port drops below relay output pressure (maximum
differential within 1.0 psi) (Figure 4).
Figure 4. Lower Pressure Transfer Relay.
RL 243 MP Multi-Purpose Relay Technical Instructions
Document Number 155-042P25
September 10, 2018
Siemens Industry, Inc. Page 5
Signal Advancing Relay
Output pressure will exceed input pressure by a constant value (as adjusted with spring
S-1) except as limited by available air supply at S-port (Figure 5).
Figure 5. Signal Advancing Relay.
Minimum Pressure
Relay
Relay output will always provide a minimum pressure as adjusted with spring S-1.
Variations in input signal below this minimum will not affect output pressure. Output
pressure will equal input pressure for any value over the minimum setting. Air supply to
S-port can be from EP valve or equivalent to provide interlock with system operation
(Figure 6).
Figure 6. Minimum Pressure Relay.
Technical Instructions RL 243 MP Multi-Purpose Relay
Document Number 155-042P25
September 10, 2018
Page 6 Siemens Industry, Inc.
Direct Acting (DA) Limit
Control
Variable pressure signal from primary controller will pass directly to relay output as long
as an equal or higher pressure is available from the limit control. Spring S-1 can be
adjusted to allow a minimum output which will not be under control of the limiting device
(Figure 7).
Figure 7. Direct Acting (DA) Limit Control.
Reverse Acting (RA)
Limit Control
Variable pressure signal from primary controller will pass directly to relay output.
Maximum relay output can be adjusted with spring S-1. An air pressure signal from the
limiting device will reduce the possible output pressure an equal amount below the
maximum setting (Figure 8).
Figure 8. Reverse Acting (RA) Limit Control.
RL 243 MP Multi-Purpose Relay Technical Instructions
Document Number 155-042P25
September 10, 2018
Siemens Industry, Inc. Page 7
Signal Inverting Relay
Input signal will pass directly to relay output until maximum output pressure is reached
(1/2 of spring setting). A further rise in input pressure will reduce output by an equal
amount (Figure 9).
Figure 9. Signal Inverting Relay.
Characterized Min.
Pressure Relay
Initial input from controller will increase relay output above minimum at a 2/1 ratio until
relay output is twice the minimum value. A further increase in input pressure will increase
the output an equal amount (1/1 ratio) (Figure 10).
Figure 10. Characterized Min. Pressure Relay.
Technical Instructions RL 243 MP Multi-Purpose Relay
Document Number 155-042P25
September 10, 2018
Information in this publication is based on current specifications. The company reserves the right to make changes in specifications and models as
design improvements are introduced. POWERS is a registered trademark of Siemens Industry, Inc. Other product or company names mentioned
herein may be the trademarks of their respective owners. © 2018 Siemens Industry, Inc.
Siemens Industry, Inc.
Building Technologies Division
1000 Deerfield Parkway
Buffalo Grove, IL 60089
+ 1 847-215-1000
Your feedback is important to us. If you have
comments about this document, please send them
to sbt_technical.editor.us.sbt@siemens.com
Document No. 155-042P25
Printed in the USA
Page 8
Installation
(See Installation
Instructions 129-121
for more information.)
Multi-Purpose Relay with integrel bracket can be installed on panels, ducts, unit
ventilators, or any other vertical or horizontal surface. Relay also can be panel mounted to
facilitate manual adjustment. Technical Bulletin 155-246 (TB 148) shows panel mounting
arrangement.
• Slotted base accommodates screws or bolts for direct horizontal mounting within
panel or on a flat wall surface.
• Integral bracket allows vertical mounting with panel or on a flat wall surface.
Dimensions
Figure 11. Dimensions in Inches (Millimeters).
Loading...