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Instruction Manual

D103032X012

L2 Controller

July 2015

10

Principle of Operation

The operation of 

L2

 controllers in combination with the sensor is based on Archimedes Principle, which states that a

body immersed in a liquid will be buoyed up by a force equal to the weight of the liquid displaced. The buoyant force
and resultant movement of the displacer in the liquid is transmitted to the controller which delivers a pneumatic signal
to a control valve.

Figure 6 shows a simple schematic of the controller and sensor. In its normal position, the counterclockwise moment
due to the weight of the displacer about pivot point O is balanced by the clockwise zero spring moment and the
counterclockwise relay zero force moment applied through lever A to the displacer rod. The weight of the displacer
decreases when the liquid level increases and the subsequent buoyant force increases causing a force imbalance
between the zero spring, relay, and displacer forces. This force imbalance is transmitted to the relay by levers A and B.
The relay compensates for the force imbalance by converting it to a pressure output to a control valve and bringing the
forces back into equilibrium.

Figure 6. Operational Schematic

DISPLACER ROD

LEVER B

PROPORTIONAL
BAND ADJUSTMENT

PIVOT
POINT O

DISPLACER

LEVER A

ZERO
SPRING

RELAY

A5592

For throttling control, the relay pressure output will be proportional to the buoyant force. For on/off control, the relay
pressure output will be either zero or equal to the supply pressure over the range of liquid level change. The liquid level
change required to fully operate the relay is adjusted by sliding the proportional band adjustment along lever A to vary
the lever ratio between levers A and B.

With reverse‐acting proportional control, the principle of operation remains the same as that for direct action;
however, the controller delivers an increasing pneumatic signal to the control valve when the liquid level falls.

Summary of Contents for Fisher L2

Page 1: ...mbly 11 Assembly 13 Replacing the Controller Relay 13 Replacing the Controller Supply Filter 13 Figure 1 Fisher L2 Liquid Level Controller W8418 1 Related Documents 14 Parts Ordering 14 Parts Kits 14 Parts List 14 Controller 14 Sensor 16 Introduction Scope of Manual This instruction manual includes installation adjustment maintenance and parts ordering information for the Fisher L2 liquid level co...

Page 2: ... 15 psig output signal and 2 4 bar for 0 4 to 2 0 bar output signal 35 psig for 6 to 30 psig output signal On Off Any desired pressure between 1 4 and 3 4 bar 20 and 50 psig Snap Acting Controller Any desired pressure between 1 4 and 5 2 bar 20 and 50 psig direct and 1 4 bar and 2 4 bar 20 and 35 psig reverse Do not use supply pressure below 1 4 bar 20 psig Supply Medium Air or natural gas 4 Stead...

Page 3: ...avity differential with standard displacer is 0 4 Minimum specific gravity differential of 0 1 is possible with special displacer consult your Emerson Process Management sales office for displacer sizing information 4 This product can be used with natural gas as the supply medium 5 Normal m3 hr Normal cubic meters per hour 0_C and 1 01325 bar absolute Scfh Standard cubic feet per hour 60_F and 14 ...

Page 4: ...RNING at the beginning of the Maintenance section of this instruction manual CAUTION If the L2 level controller is installed on a vessel that is to be shipped to a different location e g skid mounted units remove the displacer and displacer rod extensions before shipment Failure to do so could result in damage to the displacer rod due to vibration and impact loading during shipment After the vesse...

Page 5: ...G Personal injury or property damage may occur from an uncontrolled process if the supply medium is not clean dry oil free air or non corrosive gas While use and regular maintenance of a filter that removes particles larger than 40 micrometers in diameter will suffice in most applications check with an Emerson Process Management field office and industry instrument air quality standards for use wi...

Page 6: ...m 1 2 inch diameter pipe for the remote vent pipe Check the vent periodically to be certain it is free of any obstructions Changing Controller Action or Mode WARNING To avoid personal injury caused by a sudden release of pressure shut off the supply pressure and bleed pressure from the supply lines before performing any procedure in this section Throttling and On Off Controller The action of a thr...

Page 7: ...CREWS SWITCH RETENTION SCREWS 1 NOTE 1 ALL FOUR SWITCH RETENTION SCREWS SHOWN ONLY ON THIS VIEW OTHER VIEWS SHOW ONLY TWO SWITCH RETENTION SCREWS IN ORDER TO ILLUSTRATE THE SWITCH CONFIGURATION B2339 1 Figure 4 Fisher L2 Snap Acting Controller Switch Positions for Changing Action SWITCH RETENTION SCREWS SWITCH RETENTION SCREWS DIRECT ACTION REVERSE ACTION NOTE 1 ALL FOUR SWITCH RETENTION SCREWS SH...

Page 8: ... MOST SENSITIVE POSITION FOR THROTTLING AND ON OFF CONTROLLER MAXIMUM SPAN LEAST SENSITIVE POSITION FOR SNAP ACTING CONTROLLER LEVER A CONTACTING THE DISPLACER ROD GB0137 2 E0787 LEVER A LEVER B SPAN LEVER GAP Preliminary Checks 1 Check the supply pressure gauge key 10 to be certain that the supply pressure is at the desired value Adjust the supply pressure as required 2 Adjust the displacer rod t...

Page 9: ...below the bottom of the displacer or at the lowest desired operating point on the displacer 3 Adjust the spring adjustment key 4 until the output is 16 to 17 psig for a 3 to 15 psig output range or 31 to 34 psig for a 6 to 30 psig output range Direct Acting On Off and Snap Acting Controllers 1 Make certain the Preliminary Checks procedure at the start of this section has been completed 2 Lower the...

Page 10: ...e increases causing a force imbalance between the zero spring relay and displacer forces This force imbalance is transmitted to the relay by levers A and B The relay compensates for the force imbalance by converting it to a pressure output to a control valve and bringing the forces back into equilibrium Figure 6 Operational Schematic DISPLACER ROD LEVER B PROPORTIONAL BAND ADJUSTMENT PIVOT POINT O...

Page 11: ... for the process before taking the controller out of service D Provide a means of containing the process fluid before removing any measurement devices from the process D Vent any trapped process pressure D Check with your process or safety engineer for any additional measures that must be taken to protect against process media Removing the Controller From the Sensor 1 Disconnect the supply and out...

Page 12: ... the pivot base key 73 retaining ring key 76 anti extrusion ring key 75 and O ring key 74 off the displacer rod Remove the O ring key 77 and backup ring key 78 from the pivot base Figure 7 Sensor GB0139 C sht 1 VIEW C C VIEW B SECTION A A C C A A B APPLY LUB SEALANT ...

Page 13: ...s possible while pushing the pivot base into the sensor connection Be sure the pivot base seats in the slots cast in the sensor connection 7 Slide the spring key 68 and spacer key 66 onto the displacer rod and secure with the hex nut key 67 Fully tighten the hex nut key 67 8 View the sensor connection from the vessel side Ensure that the pivot body arms remain aligned with the pivot base arms the ...

Page 14: ...8 WARNING Use only genuine Fisher replacement parts Components that are not supplied by Emerson Process Management should not under any circumstances be used in any Fisher instrument Use of components not supplied by Emerson Process Management may void your warranty might adversely affect the performance of the valve and could cause personal injury or property damage Parts Kits Description Part Nu...

Page 15: ...oller July 2015 15 Figure 8 Fisher L2 Liquid Level Controllers VIEW A A SNAP ACTING CONTROLLER THROTTLING AND ON OFF CONTROLLER RELAY ASSY APPLY LUB SEALANT GB0137 D SNAP ACTING CONTROLLER RELAY ASSEMBLY THROTTLING AND ON OFF CONTROLLER A A ...

Page 16: ... 71 Drive Screw stainless steel 72 Pivot Body CB7CU 1 17 4PH SST 73 Pivot Base CF8M 316 SST 74 O Ring 3 fluorocarbon 75 Anti Extrusion Ring 3 PTFE 76 Retaining Ring 304 SST 77 O Ring 3 fluorocarbon 78 Backup Ring 3 fluorocarbon 79 Lithium grease not furnished with sensor 80 Instruction Tag 82 Extension S31600 Recommended spare parts 1 Included in Controller Repair Kit 2 Included in Relay Repair Ki...

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