Pressductor Pillowblock Load Cells Vertical Measuring PFCL 201 User manual

Spare Parts

Users are recommended to keep the following spare parts in stock:

 • One load cell of correct type and size.

 • One connector complete with cable (for PFCL 201C)

Table 5  Ordering numbers for Load Cell PFCL 201

Load cell PFCL 201C  5,0 3BSE027070R5

Load cell PFCL 201C 10,0 3BSE027070R10

Load cell PFCL 201C 20,0 3BSE027070R20

Load cell PFCL 201C 50,0 3BSE027070R50

Load cell PFCL 201CE 5,0 3BSE027062R5

Load cell PFCL 201CE 10,0 3BSE027062R10

Load cell PFCL 201CE 20,0 3BSE027062R20

Load cell PFCL 201CE 50,0 3BSE027062R50

Load cell PFCL 201CD 5,0 3BSE029774R5

Load cell PFCL 201CD 10,0 3BSE029774R10

Load cell PFCL 201CD 20,0 3BSE029774R20

Load cell PFCL 201CD 50,0 3BSE029774R50

General

It is important to be thoroughly familiar with the description of operation in 2 Description before starting fault tracing.

Interchangeability

The load cells are factory calibrated and can be replaced directly with another load cell of the same type. The only adjustment required after load cell replacement is zero adjustment in the control unit.

Fault Tracing Procedure

The measuring equipment can be divided into four parts:

• The mechanical installation. 

• The load cell. 

• The junction boxes and the cabling.

• The control unit (see the control unit manual).

The fault symptoms indicate in which part the fault lies.

• Faults in the mechanical installation often result in an unstable zero point or incorrect sensi tivity. If a fault follows something else in the process, such as temperature, or can be linked to a particular operation, it probably originates from something in the mechanical installation.

• Load cells are extremely robust and can withstand ten times their nominal load in the meas uring direction. If a load cell has nevertheless been so overloaded that its data have been altered, this is probably due to an event in the mill, such as strip breakage. On excessive overload the first thing that happens is that the zero point shifts.

• Problems such as interference or unstable zero point may be caused by wiring faults. Some malfunctions may be due to the proximity of cables that cause interference. Incorrect instal lation, such as imbalance in a cable or screens earthed at more than one end may cause the zero point to become unstable. Cables are subject to mechanical wear, and should be checked regularly. The junction box should also be checked, especially if it is subject to vibration.

• A fault in the control unit usually causes intermittent loss of a function. It is unusual for the control unit to cause stability problems. Faults in connected units may affect the operation of the control unit. For further details see the control unit manual.

Fault Tracing in the Mechanical Installation

There are a number of parts in the mechanical arrangement that can cause faults. The extent to which these faults are repeatable differs. Possible causes fall into the following groups.

• Defective mounting surface, stand or adapter plates. 

• Force shunting. 

• Insufficient mounting of load cell and adapter plates.

• Rolls and bearings. • Driven roll.

Defective Mounting Surface, Support or Adapter Plates

An unmachined or poorly machined mounting surface, which is uneven, may cause bending or twisting of the load cell. This may result in instability of the zero point.

Force Shunting

Force shunting means that some of the force is diverted past the load cell. This may be caused by some kind of obstruction to the force through the load cell. The connecting cables, for example, have been incorrectly installed and are preventing movement. Another possible cause is that the roll is not free to move in the direction of measurement, possibly because something is mounted too close to a bearing housing, or because an object has worked loose and become trapped between the bearing housing and adjacent parts.

Force shunting causes the strip tension indication to be lower than the actual strip tension.

Fastening of Load cell and Adapter Plates

Screw joints that have not been properly tightened or have lost their pre-tightening force, cause sliding at the mating surfaces. Fastening of the load cell is especially critical. If a load cell is not properly secured, the zero point will be unstable. Sliding between other surfaces may cause the same symptoms.

Rolls and Bearings

An incorrectly designed bearing arrangement may give rise to high axial forces. The roll should be f ixed at one end and free at the other. If both ends are fixed, there will be a high axial (thrust) force due to expansion of the shaft with rising temperature. Even a correctly designed bearing arrangement may deteriorate with time; bearings become worn, and so on. This may give similar symptoms, such as slow zero point drift between cold and hot machine, or sudden jumps in the signal.

Driven Roll

A source of error that is seldom suspected is the roll itself. The effect is especially critical when measuring forces on the load cell are relatively low. Long drive shafts with their associated universal joints may cause unstable signals if they are not properly maintained. It is important to lubricate universal joints. Longitudinal expansion of the drive shaft should also be taken into account. Since such expansion is often taken up by splines, these must also be lubricated. The symptoms are instability of the signal, for instance jumps in the signal during slow running.