Pressductor Pillowblock Load Cells Vertical Measuring PFCL 201 User manual

The primary winding is supplied with an alternating current which creates a magnetic field around the primary winding. Since the two windings are at right angles to each other, there will be no mag netic field around the secondary winding, as long as there is no load on the sensor.

When the sensor is subjected to a mechanical force in the direction of measurement, the propaga tion of the magnetic field changes so that it surrounds the secondary winding, inducing an alternat ing voltage in that winding.

The control unit converts this alternating voltage into a DC voltage proportional to the applied force. If the measurement force changes direction, the sensor signal changes also polarity.

Mounting Arrangement

When choosing a mounting arrangement it is important to remember to position the load cell in a direction that gives sufficient measuring force (FR) to achieve the highest possible accuracy.

The load cell has no particular correct orientation; it is positioned in the orientation best suited for the application, bearing in mind the positions of the screw holes. The load cell can also be installed with the roll suspended under the load cell.

The load cell has the same sensitivity in both tension and compression, so the load cell can be installed in the easiest manner.

Typical mounting arrangements are horizontal and inclined mounting.

Coordinate System

A coordinate system is defined for the load cell. This is used in force calculations to derive force components in the load cell principal directions.

Where direction designations R, V and A are recognized as suffixes for force components, F, this represents the force component in the respective direction. The suffix R may be omitted, when measuring direction is implied by the context.

Horizontal Mounting In the majority of cases horizontal mounting is the most obvious and simplest solution. Stand, mounting surface and shims (if required) are simple and cheap to make. When calculating the force, the equations below must be used: 

 FR = T × (sin α + sin β) FRT = Tare FRtot = FR + FRT = T × (sin α + sin β) + Tare FV = T × (cos β - cos α) FVT = 0 FVtot = FV + FVT = T × (cos β - cos α) + 0 = T × (cos β - cos α) where: T = Strip tension

 FR = Force component from strip tension in measurement direction, R FRT = Force component from Tare in measurement direction, R FRtot = Total force in measurement direction, R FV = Force component from strip tension in transverse direction, V FVT = Force component from Tare in transverse direction, V FVtot = Total force in transverse direction, V Tare = Force due to tare weight α = Deflection angle on one side of the roll relative the horizontal plane β = Deflection angle on the other side of the roll relative the horizontal plane

Inclined Mounting

Inclined mounting means arrangements in which the load cell is inclined relative to the horizontal plane. In some cases this is the only option. When calculating the force, the equations below must be used:

FR = T × [sin (α - γ) + sin (β + γ)] FRT = Tare × cos γ FRtot = FR + FRT = T × [sin (α - γ) + sin (β + γ)] + Tare × cos γ FV = T × [cos (β + γ) - cos (α - γ)] FVT = - Tare × sin γ FVtot = FV + FVT = T × [cos (β + γ) - cos (α - γ)] - Tare × sin γ γ = 90° - φ

where:

T = Strip tension FR = Force component from strip tension in measurement direction, R FRT = Force component from Tare in measurement direction, R FRtot = Total force in measurement direction, R FV = Force component from strip tension in transverse direction, V FVT = Force component from Tare in transverse direction, V FVtot = Total force in transverse direction, V Tare = Force due to tare weight α = Deflection angle on one side of the roll relative the horizontal plane β = Deflection angle on the other side of the roll relative the horizontal plane φ= Angle for measurement direction relative the horizontal plane γ = Angle for load cell mounting surface relative the horizontal plane

The load cell is supplied with a 0.5 A, 330 Hz alternating current. The secondary signal is calibrated for the correct sensitivity with a voltage divider R1 - R2, and temperature compensation is provided by thermistors T. All impedances on the secondary side are relatively low. The output impedance is typically 9-12 Ω , which helps to suppress interference.

General

The equipment is a precision instrument which, although intended for severe operating conditions, must be handled with care. The load cells should not be unpacked until it is time for installation.

To achieve the specified accuracy, the best possible reliability and long-term stability, the load cells must be installed in accordance with the instructions below. See also 

 • The foundation for the load cell must be made as stable as possible. A resilient stand lowers the critical frequency of the measuring roll and bearing arrangement.

 • The surfaces closest to the load cell, and other surfaces that affect the fit, must be machined f lat to within 0.05 mm. 

 • There must not be any shims immediately above or below the load cell, as this may adversely affect the flatness. Instead, shims may be placed between the adapter plate and the foundation or between the adapter plate and the bearing housing.