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Electronic Station Management with pilot series RMG 638

General Description

638.00 edition 01/2001

Serving the Gas Industry - WORLDWIDE


Electronic Station Management with pilot series RMG 638 1. Gas pressure regulators with superordinate electronic control loops Gas pressure regulators normally operate without auxiliary energy. The power required for adjusting the valves (auxiliary power) is taken from the controlled system or the pressure drop between inlet and outlet. The increasing trend towards the integration of gas pressure regulating stations into a central network management system in order to improve network utilisation and to optimise gas supply etc. requires facilities for linking pneumatic valves and electronic control systems. RMG has developed a special equipment design for this interface. The main functional units of the electropneumatic control are a pneumatic multi-stage pilot, a pulse modulator and a higher-level automation system. The automation system is equipped with special software for electro-pneumatic control. The linking of the higherlevel automation system with the pneumatic control loops on the gas pressure regulator ensures that the gas network is supplied independently of the electronics. Even in the event of a power failure, the pneumatic components ensure that the supply is maintained. A lower pressure limit value (ensuring reliable supply) and an upper pressure limit value (max. operating pressure) are monitored via conventional DIN-DVGW approved technology. Between these two limits any pressure or flow control tasks can be carried out as specified by the higher-level automation system or by process computers. The complete electro-pneumatic regulator system was certified by DVGW under the registration number DG4301AS0607.

The RMG 638 electro-pneumatic pilot consists of function modules mounted on a common base plate: 1st stage: auxiliary pressure stage 2nd stage: control stage for minimum outlet pressure pamin 3rd stage: control stage for maximum outlet pressure pamax 4th stage: electro-pneumatic control stage as an interface between the pneumatic system and the higher-level automation system

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Electronic Station Management with pilot series RMG 638 2. RMG 638 pilot

Proportional controlmagnet Measuring line loading pressure line

Base plate Start-up valve Discharge line Pre-throttle vent line Fine filter RMG 905 10 000 159

Inlet pressure line

Automatic load limiting stage

1st control stage Pamin

2nd control stage Pamax

3rd electro-pneumatic control stage

The pneumatic pressure control stages automatically monitor the set limit values. If these limit values are reached due to the operating behaviour of the installation, the pressure control stages take over and keep the outlet pressure constant. Switching between the electro-pneumatic control stage (operated by the electronic control) and the pressure limitation through the control stages is carried out automatically and smoothly in both directions.

Inlet pressure Control pressure Auxiliary pressure Outlet pressure Atmospheric pressure

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Electronic Station Management with pilot series RMG 638 2.1 Load limiting stage The inlet pressure is fed via the RMG 905 fine filter and the adjustable pre-throttle and is available in the chamber of the control pressure and the area in front of the amplifying nozzle of the load limiting stage. At the double diaphragm system, the setpoint value will be compared with the actual value. In this pilot stage, the controlled auxiliary pressure is applied the top surface of the diaphragm via internal connection. The setpoint spring and the outlet pressure applied via the measuring line act on the lower side of the doublediaphragm system (for this purpose, the load limiting stage stage has a seal below the spring chamber). The outlet pressure force together with the force of the setpoint spring determines the auxiliary pressure which is balanced to the upper surface of the diaphragm. Even if the outlet pressure changes, the auxiliary pressure is kept constant above the outlet pressure. This auxiliary pressure is available as intermediate pressure to the downstream stages and the electro-pneumatic control stage. By carrying along the auxiliary pressure above the outlet pressure, amplification changes at the downstream stages are eliminated.

2.2 Control stage for minimum outlet pressure pamin This stage compares the outlet pressure on the upper surface of the diaphragm with the setpoint value. Normally, the outlet pressure force is greater than the spring force, and the amplifying valve is shut. The intermediate pressure continues to flow to the control stage for maximum outlet pressure and to the electro-pneumatic control stage of the pilot. Should the operating conditions cause the outlet pressure to fall, the amplifying valve opens and enables a discharge into downstrieam pipeline via the direct outlet line once the set minimum value of the outlet pressure is reached, thus reducing the control pressure above the actuator diaphragm via the control stage. The pamin stage thus takes over the control function and keeps the outlet pressure constant. The electro-pneumatic control stage in the pilot is by passed. In terms of the control task, the pamin stage has a higher priority than other control loops such as qn, qB, gas supply optimisation etc.

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Electronic Station Management with pilot series RMG 638 2.3 Control stage for maximum outlet pressure pamax The outlet pressure is monitored by comparison of set spring force setpoint value and the outlet pressure on the control diaphragm. As the outlet pressure is normally lower than the set maximum pressure, the amplifying valve is in open position. Within this control stage, the auxiliary pressure is normally transferred directly to the electropneumatic control stage. If the outlet pressure rises and reaches the setpoint limit, the amplifying valve closes and controls the transfer of the intermediate pressure to the control stage so that the outlet pressure limit in the controlled system does not be exceeded. Once the outlet pressure decreases, the electro-pneumatic control stage will take over control automatically .

2.4 Electro-pneumatic control stage The electro-pneumatic control stage is controlled via the automation system. When converting from electrical to pneumatic signals, the standardized electrical signal of 0/4 - 20 mA from the automation system is initially converted to a 24 VDC pulse signal via a pulse modulator. Depending on the pulse length, the voltage pulses generate a current through the proportional control magnet. The current generates a magnetic field in the coils, which exerts a force in the solenoid. Via a mechanical device, the force generated by the proportional control solenoid acts on the top surface of the double diaphragm system of the electro-pneumatic control stage, where it balances the force of the setpoint spring. If a control deviation occurs in the higher-level automation system, i.e. in the control loop, the magnetic force and thus the distance between nozzle and baffle plate will change. The change in the discharge of the auxiliary pressure causes a proportional variation of the control pressure and thus a change of the opening in the regulator. The gas volume and/or pressure in the controlled system are matched to specified setpoint value.

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Electronic Station Management with pilot series RMG 638 3. Setting the Pneumatic Pilot 3.1 Automatic load limiting stage: - The load limiting pressure should be set to the load limiting pressure determined at start-up.

3.2 pamin stage - Switch automation system to manual operation - Preset setpoint y of 0 % - Close downstream isolating valve - Open downsrieam bleed valve to atmosphere - Set the desired pressure setpoint at the pamin stage - Once the pamin stage has been set, close the downstream bleed line - Open the downstream valve - After switching the automation system from manual to automatic operation, the system will automatically switch to control operation

3.3 pamax stage - Switch automation system to manual operation - Preset a manipulated variable y of 0 % and close the solenoid valve in the setpoint pressure control line - Close downstream isolationg valve - Open downstream bleed valve to atmosphere (SCS 2001 automatically opens the solenoid valve) - Then open the solenoid valve in the loading pressure line and preset a manipulated variable y of 100 %; - Set the pamax stage to the desired pressure value - Then reset the manipulated variable y to 0 % - Close downstream bleed line - Open downstream isolating valve - After switching the automation system from manual to automatic, the system will automatically switch to control operation

3.4 Electro-pneumatic control stage - Switch automation system to manual operation - Preset a setpoint y of 0 % - Close downstream isolating valve - Open downstream bleed valve to atmosphere - First, the setpoint spring of the electro-pneumatic control stage is put under tension. This is done by turning the setpoint screw clockwise until the mechanical end stop is reached - Open the solenoid valve in the loading pressure line and preset a manipulated variable y of 50 %

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Electronic Station Management with pilot series RMG 638 Setting the electro-pneumatic control stage (continued) - Then turn the setpoint screw of the electro-pneumatic control stage counter clockwise until (within one turn) the outlet pressure begins to rise - Then turn the setpoint screw back again (one turn); the outlet pressure should fall again - Set the setpoint screw between these two positions (usually a 180-degree turn) and secure. The outlet pressure should be kept with this setting between the set pressure values of pamin and pamax. To ensure that none of the upstream pilot stages limits the control pressure. - Preset a manipulated variable y of 0 % - Close the pressure bleed line in the outlet - Open downstream isolating valve - After switching the automation system from manual to automatic, the system will automatically switch to regulator operation.

4. Description for RMG 110a (pulse modulator) The pulse modulator is used for converting an electrical standardized signal from the higher-level automation system (0/4 - 20 mA or 0 - 10 V) into a 24 V pulse signal for controlling the electro-pneumatic control stage. A 24 V direct current is required to supply the RMG 110a. This has a maximum current consumption of 1.5 A.

4.1 Configuration options: Several DIP switches are provided to select different operating modes RMG standard: 4 - 20 mA The characteristic curve properties (falling or rising characteristic curve) can be selected via a jumper. RMG standard: rising characteristic curve The modulation frequency is usually set to a "low frequency"; and is then approx. 50 Hz. The operating range of the pulse modulator is defined by the potentiometer settings of the zero point, the range and the precise frequency. These settings are the factory settings when the device is delivered. RMG standard: zero point, range and frequency set. The proportional control solenoid is relieved through the shutdown function, if the manipulated variable of the higher-level automation system is < 3% RMG standard: shutdown function activated.

4.2 Adjusting the electro-pneumatic control stage to the pulse modulator â&#x20AC;˘ See setting of the pneumatic pilot, point 3.4

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Electronic Station Management with pilot series RMG 638 4.3 Modulator RMG 110a

ON

Magnetstrom

MP3 MP1

- SOLL + - MAG + - VDC +

output for el. regulator

GND

P3 FREQ

a Frequenz

modulator aux. power current cons.

P2 OFFSET

Auxiliary power 24 VDC, 1.5 A

MP2

5 6

normal P1 SPAN J1

Proportional magnet

S

3 4

1234

Setpoint value (manipulated variable coming from control system)

OFF

1 2

invers

37

Connection diagram:

Dimensions: DIP switches for setpoint selection S1

108

Auxiliary power supply 24 VDC; 1.5 A Proportional magnet at electro-pneumatic control stage Output el. control system 0/4 - 20 mA

Auxiliary power: Current consumption: Input signal: Output signal: Pulse frequency: Protection class: Response characteristics: Rising Falling

S3 Off 0-10 V Off 0-20 mA On 4-20 mA

DIP switches for "Shut Down" S4 active inactive

P1 = range P2 = offset P3 = frequency

Snaps onto DIN rail

Technical data:

Off On On On On Off

On Off

75

S2

24 VDC max. 1.5 A 0 / 4 - 20 mA or 0 - 10 V galvanically separated 24 V pulse signal 50 Hz IP 20

Dimensions:

H x W x D 75 x 37 x 108

General:

Connection via plug-in screw-type terminals Snaps onto DIN rail RMG Part-No.: 80024322

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Electronic Station Management with pilot series RMG 638 4.4 Conversion of the standard signal into a pulse width modulated pulse signal via the pulse modulator RMG 110a

Input signal - current (e.g. 4 - 20 mA) I 20 mA

10 mA

4,5 mA

0 mA

Shut-down

Time axis t

Output signal - voltage

Energy area

U 24 V

0V Time axis t

f

10

f = 50 Hz


Electronic Station Management with pilot series RMG 638 4.5 Control of the control stage via proportional magnet

Magnetic force

Range

[N] 60

er

r

pe

s re

ve

Up

45

Vss. Y = S S = stroke

ge

35 ing

n ra

at er

Op

25 e rv

se

e rr

we Lo

10

n ow

-d

t hu

S

0

10

23

30

40

50 AP

AP = operating point

60

70

80

90

100 Y - signal in % regulator manipulated variable 4 - 20 mA

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Electronic Station Management with pilot series RMG 638 5. Operating Principle of the Four-Channel Electronic Override Control with Automation System SCS 2001 (Protronic 500) (continuous manipulated variable) Example according to process flow diagram (755.56) and diagram (915.35):

Control loop

Control task

Priority

1

Actual flow qB (meter protection)

highest priority

2

Nominal flow qn

third-highest priority

3

Outlet pressure pamin

second-highest priority

4

Outlet pressure pamax

third-highest priority

Assumption: â&#x20AC;˘ consumption = constant, gas meter is installed in the downstream pipeline â&#x20AC;˘ the outlet pressure xpa is controlled within the limits of electronic pamin - and pamax control loop â&#x20AC;˘ due to the operating conditions (xpa and xqn), the operating flow limiter qBmax is currently not active.

qn control: As long as the autlet pressure does not exceed the limits given by pneumatic pamin and pamax-stage of the pilot, the nominal flow qn can be varied from the dispatching centre via external setpoint signal or via internal setpoint value of SCS 2001. If the consumption in the gas network equals the supplied volume, the outlet pressure remains unchanged and the qn controller determines the manipulated variable. If the supply into the gas network is increased, the outlet pressure pa will also increase, and the actual flow qB will decrease accordingly.

pamax control: If the outlet pressure pa reaches the specified setpoint value wpamax of the pressure controller pamax, the pamaxcontroller will take over by limiting the outlet pressure due to its setpoint. Supplied and consumed volumes are then equal.

qn control: If the supply qn is reduced below the consumed volume, the outlet pressure pa will decrease continuously.

pamin control: If the outlet pressure pa reaches the setpoint value wpamin of the pressure controller pamin, the pamin-controller will take over by limiting the outlet pressure. The nominal flow increases to the volume, requested by comsumer due to its setpoint.

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Electronic Station Management with pilot series RMG 638 qB control: If the setpoint for nominal flow qn is high and the outlet pressure is low, the actual flow qB could reach the setpoint of the flow controller qB. In this case the qB-controller will take over control by limiting the actual flow due to its setpoint (meter protection). qn control: The smooth transition to qn control occurs as soon as the nominal flow reaches the specified qn setpoint value (outlet pressure pa at the gas meter has increased).

pamax control: If the outlet pressure pa increases up to the specified setpoint value wpamax of the pressure controller pamax, the outlet pressure will be limited again to the specified setpoint value and take over the control. Supplied and consumed volume are once again equal.

Special case Intermittent operation: If the consumption is lower than nominal flow setpoint, the pressure in the downstream network will increase until the pressure controller pamax limits the flow to the consumed volume, thus keeping the outlet pressure constant. If the consumption is lower than meter range limit qBmin set at the automation system, the system will switch off until the outlet pressure has fallen to a low pressure limit value that is freely adjustable at the automation system. The supply will then once again follow the specified standard flow setpoint value wqn. The intermittent operation procedure is repeated until the delivery volume is above the lower meter range limit. The electronic control will cease operation if the electricity supply fails or if a measuring signal violates its limit range. The valve automatically moves to the safe closed position, until the outlet pressure has decreased to the setpoint value of the pneumatic pamin stage. This will automatically take over control and keep the outlet pressure constant irrespective of the flow rate.

Note! Once the pneumatic pamin pilot takes over, the meter is no longer protected.


Electronic Station Management with pilot series RMG 638 Graph of the process variables over time for different operating conditions of a four-way override control, gas meter in the outlet area (RMG sheet no (915.35)

qn-

qn-control qn-control

qn-control

pamax -control Xqn = consumptioin

Xqn > consumptioin

Xqn < consumptioin

control

pamin -control Xqn = consumptioin

qB-

control Xqb=WqB

Xqn delivery

pamax-control Xqn = consumptioin

Xpa

WqB

Wqn

Xqn consumptioin consumptioin

XqB

Xqn XqB XqnA Xpa

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= nominal flow (supply into the gas network) = actual flow = gas consumption in the network = outlet pressure (network pressure)

Xqn

Wqn

WqB Wqn Wpamax Wpamin

= setpoint value for actual flow (meter protection) = setpoint value for nominal flow = setpoint value for max. outlet = setpoint value for min. outlet

XqB


Non-hazardous area Hazardous area

fine filter

Measuring transducer

el. pneum. regulator

breathing line

base plate

Discharge line

Measuring line

closed at zero curr.

2/2 solenoid valve

Proportional solenoid

electro-pneumatic control stage

Regulator

control stage

Setpoint pressure line

control stage

pulse signal

Pulse modulator

gas meter

Volume converter

Measuring transducer

Supply unit

Outlet slide valve

Isolation amplifier

Potential-free signal connection to SCS 2001

* Configure flow signals without delay ** Setpoint assignment via standardized signal or RS 484 (Modbus RTU)

Electronic Station Management with pilot serie RMG 638

Electronic system control with flow regulation qn, meter protection control qBmax, intermittent operation qBmin, outlet pressure regulation pamax and pamin with pneumatic pressure protection

Discharge valve

Inlet pressure line

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We supply you with products for gas pressure regulation: RMG REGEL + MESSTECHNIK GMBH Osterholzstrasse 45, D-34123 Kassel, Germany Telephone (++49) 561 5007-0 • Fax (++49) 561 5007-107 gas pressure regulators and safety devices

RMG-GASELAN Regel + Meßtechnik GmbH Julius-Pintsch-Ring 3, D-15517 Fürstenwalde, Germany Telephone (++49) 3361 356-60 • Fax (++49) 3361 356-836 gas pressure regulating equipment, displacement meters, complete stations

Bryan Donkin RMG Gas Controls Ltd. Enterprise Drive, Holmewood, Chesterfield S42 5UZ, England Telephone (++44) 1246 501-501 • Fax (++44) 1246 501-500 gas pressure regulating equipment, below ground gas control modules

Bryan Donkin RMG Co. of Canada Ltd. 50 Clarke Street South, Woodstock, Ontario N4S 7Y5, Canada Telephone (++1) 519 5398531 • Fax (++1) 519 5373339 domestic regulators and safety devices

The other RMG Companies: RMG Messtechnik GmbH Otto-Hahn-Strasse 5, D-35510 Butzbach, Germany Telephone (++49) 6033 897-0 • Fax (++49) 6033 897-130 turbine meters, vortex meters, correctors, flow computers, odorizers

Karl Wieser GmbH Anzinger Strasse 14, D-85560 Ebersberg, Germany Telephone (++49) 8092 2097-0 • Fax (++49) 8092 2097-10

Betriebsstelle Beindersheim Heinrich-Lanz-Strasse 9, D-67259 Beindersheim/Pfalz, Germany Telephone (++49) 6233 3762-0 • Fax (++49) 6233 3762-40 data logging, monitor systems, danger alarm systems

WÄGA Wärme-Gastechnik GmbH Osterholzstrasse 45, D-34123 Kassel, Germany Telephone (++49) 561 5007-0 • Fax (++49) 561 5007-207 design and assembly of gas pressure regulating and metering stations

The RMG Group of Companies on the internet: http://www.rmg.de

Serving the Gas Industry - WORLDWIDE

We reserve the right for technical changes


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