Fault Tracing of Load Cells, Junction Boxes and wiring
The load cell is very robust and can withstand high overloads. The data of a Pressductor load cell does not change slowly, but in steps, usually in connection with an event in the mill. Excessive overloading usually results in permanent shifting of the zero point. Poor contact in the junction box causes intermittent faults. Both sensitivity and zero point may vary. Check all screw terminals. Do not use pins crimped to the connecting wires, as these often work
loose after a time.
The cabling, especially the cable to the load cell, is the part that is most exposed to damage.
Since the resistance of the load cell windings is low, it is easy to check the load cells and cabling from the control unit.
Typical readings are 2 Ω for the resistance of the primary winding and 9-12 Ω for the output impedance of the secondary winding.
Insulation faults in the cabling or the load cell may cause incorrect sensitivity or unstable zero point.
When the load cell circuits have been isolated from earth and from the control unit at the disconnectable terminals, it is easy to measure the insulation from the control unit.
If the cables are not routed correctly, they may pick up interference from other cables.
Pressductor PillowBlock load cells
Introduction
ABB’s Pressductor® PillowBlock load cells are sensitive and accurate yet rugged, reliable andcompact. The performace of the Pressductor PillowBlock load cells is unsurpassed for paper mill applications characterized by heavy rolls, high speeds and severe conditions – in some instances they are the only viable option. They can withstand high overloads and vibrations, and operate over a wide range of tensions.
The well-proven Pressductor load cells combined with the tension electronics, offer an easy-to-use/ user-friendly web tension measurement system with superior long term performance leadingto higher productivity and product quality and higher profit for the web producer.
Increased process uptime
In a web process running continuously, every minute of production time is precious. Even so, no production line runs without downtime. With Pressductor PillowBlock load cells the risk of web breaks can be reduced to a minimum, thus leaving as much time as possible for real production.
Thanks to a strong and stable signal deriving from the Pillow-Block load cells, the upcoming web breaks are kept to an absolute minimum level.
Tighter product tolerances
The ability to produce web to tighter tolerances minimizes the costs associated with nonconforming web. It also increases the web producer’s accessible market to include products with tighter tolerance requirements.
Pressductor PillowBlock load cells 50 years of experience
Minimize maintenance
Share the experience, of virtually maintenance-free load cells, with thousands of other PillowBlock users. A robust load cell design with no fragile or ageing components makes this possible.
Thanks to its robust design, the PillowBlock load cells work consistently for many years without any need for maintenance, also in the toughest paper mill applications.
Fast access to support and service
ABB provides customers with superior distinctive after sales service that really differentiates from the competition. You obtain advanced solutions to problems, service and professional consultation through our After Sales Service program. Expert engineers with extensive experience of all types of Force Measurement products are available to assist you through our world-wide network.
There is a PillowBlock load cell suitable for most web processing machinery used in the paper processing industries
In the paper industry, the PillowBlock load cells are ideal in wire, press and dryer sections as well as in coaters, calenders and winders.
In the converting industry, the PillowBlock load cells have proven their superior performance in laminator and coater machinery.
The Pressductor difference
Like ABB’s other load cells based on Pressductor
Technology, PillowBlock load cells rely on electromagnetic changes in the transducer, not on physical movement, to sense fluctuations in web tension. The Pressductor Technology operating principle provides exceptional improvements in load cell performance characteristics, including reliability (notably absence of drift), durability, repeatability, and wider measurement range.
Machined from a solid block of steel, the load cells are rugged and stiff, affording high overload protection as well as an extended measurement range above the nominal load. And they do not contribute to machine vibration, even at high speeds.
Since the transducer action – the magnetic flux
– takes place inside a steel core, environmental factors like dirt or fluids can’t degrade performance and reliability. These stainless steel load cells don’t require any physical seals.
Furthermore, low transducer impedance
– less than a couple of ohms – helps eliminate susceptibility to radio-frequency and electromagnetic interference.
Pressductor PillowBlock load cells Ideal for paper and converting industry
Designers appreciate:
• Remarkably high spring constant
• Wide measurement range
• High reliability
Operators value a load cell with:
• No drift
• No need for recalibration
• No failures
• High reliability
Measurement essentials
Keeping the tension constant in web processes is essential for high product quality and productivity.
Continuously measuring the tension is an obvious prerequisite for tension control. Drives and operator instruments need quick and accurate input to regulate tension levels and monitor machine performance.
Most web processing lines put a premium on long-term reliability, in addition to accuracy and overall performance. The measurement system, after all, is the front line of machine control, exposed to all the rigors of the operating environment. The costs associated with downtime and poor product bring out the true value of its components.
Quality measurement technology for superior tension control that will keep your processing
lines productive and producing top-notch output
– that’s what you can expect from us. We’re entirely devoted to providing process measurement systems and services, and we have 60 years of experience in the field. We are the experts in web and strip tension as well as force measurement for virtually any purpose.
Selecting and sizing load cells
The two types of ABB PillowBlock load cells are designed for either conventional vertical force measurement or for sensing the horizontal force component that may arise as the processed material partially wraps around a measurementroll.
Using the horizontal load cells can be quite advantageous. By design, they can be made exceptionally sturdy, rugged, and stiff.
So, requirements for recalibration, other maintenance, or replacement are negligible, and they do not contribute to machine vibration.
Since they don’t measure the tare weight, but just the horizontal force component of the web tension, they can be sized smaller than otherwise possible,measuring tension with greater accuracy.
Application requirements may dictate the selection of a vertical load cell. But whenever an adequate horizontal force component is present (or can be developed), the horizontal load cell should be considered.
The size, or nominal load, of a load cell is contingent on the anticipated force it will measure. When a vertical load cell is mounted horizontally (the most common arrangement), the measurement force (FR) is a function of the tension in the web (T), the deflection angles (α and β), and the tare weight of the roll and bearings (Tare).
The horizontal load cell senses the web tension’s (T) horizontal component (FR); not the vertical force (FV).
In this scenario, the measurement force (FR) is a function of only the tension in the web (T) and the web angles (α and β). Since the tare force (the weight of the deflector roll and bearings) will not be measured, it can be very large compared to the web tension without affecting the accuracy of the tension measurement.
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