Gauge head PMGG201

Due to its heavy duty construction and the stability of its measuring principle, the MTG Box Gauge can be used in locations where it is impossible for other gauges to function.

Function
The MTG Box Gauge is based on PEC technology, which uses magnetic fields for measurement of strip thickness. The interaction between an applied magnetic field and the electrically conductive strip indicates thickness – without influence from the material composition.

The pulsed magnetic field is generated and measured by sturdy electric coils placed just below the cover plate. Since the magnetic field penetrates everything except metal, the coils can be protected by a heavy-duty fiberglass reinforced epoxy plate.

Traceable thickness measurement
The MTG Box Gauge is delivered calibrated and ready to use. Twelve calibration plates are supplied with the system for verification and adjustment of the complete measuring range.

These calibration plates ensure that the gauge measures absolute thickness and thickness deviation according to traceable standards for many years of operation. A normal interval for calibration is 6 months and takes only 20 minutes to perform.

Robust design
The aluminium-bronze housing has superior mechanical and chemical characteristics and provides robust protection for the gauge, making it optimal for harsh rolling mill environments.

The gauge is mounted on a vertically moving frame, automatically adjusting its position to maintain an optimal measuring distance.
The movement is operated with hydraulic valves.


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Data
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Data

Type PMGG 201
Minimum/Maximum thickness 0.5 - 8 mm (20 - 315 mil)
High pass mode (for Feed Forward) 0.2 - 0.6 mm (8 - 24 mil)
Measured alloys Aluminium, clad aluminium and other nonferrous alloys
with resistivity range 27 - 65 nΩm
Repeatability ±0.05% (not better than 0.3 μm (12 μin)
Accuracy 1 ±0.05% (not better than 0.5 μm (20 μin)
Total Accuracy 2 ±(0.05% +1.5 μm (59 μin)
Total Accuracy clad measurement 3 ±(0.05% +2 μm (79 μin)
Oil on strip No influence
Measuring distance 15 mm (590 mil)
Minimum strip width 500 mm (20 in)
Minimum distance from strip edge 100 mm (4 in)
Measuring area Ø 80 mm (3.15 in)
Strip position changes > 1 mm/s / >39 mil/s ±5 mm (± 197 mil)
Strip slope ±6°
Gauge holder stroke length 50 mm (2.0 in)
Updating time
 5 ms
Operation temperature
 +5 to +70°C (+41 to +158°F)
Degree of protection IP 65
Power supply (from the control unit) 24 V DC, max 3 A (48 V AC, max 5A)
Dimensions
Gauge head L 352 x W 228 x H 209 mm
(L 13.9 x W 9.0 x H 8.2 in)
Gauge head and holder L 495 x W 228 x H 353/403 mm
(L 19.5 x W 9.0 x H 13.9/15.9 in)
Weight
Gauge head 22 kg (48.5 lb)
Gauge holder 48 kg (105.8 lb)

1) Accuracy = Calibration accuracy, i.e. accuracy after calibration, measured on a calibration plate.
2) Total Accuracy = Accuracy after calibration, measured on an arbitrarily selected plate/strip at normal mill operating conditions, i.e. with mill coolants, temperature variations, pass line variations and alloy composition variations.
3) Provided that input clad parameters are correct.

Application

The MTG Box Gauge is designed for use in aluminium breakdown mills and aluminium continuous casters. In rolling mills, the MTG systems are connected to AGC systems for feedback, feedforward and massflow control.

Increased mill production time
In a production process running 24 hours a day, every minute of production time is precious. Thanks to its alloy independence, the MTG can increase available production time by eliminating the need to stop for standardization and calibration.

The hydraulic positioning system allows the gauge to measure almost instantaneously when tension comes on, thus optimizing the strip length under thickness control.

Tighter strip tolerances
The ability to produce strip to tighter tolerance maximizes productivity and minimizes the costs associated with non-conforming strip. It also increases the strip producer’s accessible market to include product with tighter tolerance requirements.

Pulsed Eddy Current technology

The MTG Box Gauge, based on PEC (Pulsed Eddy Current) technology, opens up new dimensions in aluminium strip gauging. Weak magnetic fields are used for measurement and the gauge is completely safe to use.

The technology is completely insensitive to anything in the measuring zone, except the metal strip. The gauge will, therefore, measure true strip thickness, unaffected by coolant, dirt, steam, air temperature variations, etc.

Since the MTG Box Gauge is material-independent, there is no need for alloy compensation and calibration.

Phase 1: Transmitting

  • An electric field is generated with a transmitting coil
  • The field is applied until it fully penetrates the strip
  • The field "energy" is stored in the air gap and in the strip
  • The amount of energy stored in the strip depends on the thickness alone - not on resistivity

Phase 2: Distance measurement

  • Fast air response just after transmit field is swithed off
  • The measurement of air gap energy corresponds to distance between coil and strip
  • Pulse time t1 is typically less than 5μs

Phase 3: Resistivity measurement

  • Response from the surface area of the strip
  • The measurement starts when the air gap signal has declined
  • The measurement of the surface response corresponds to resistivity and is dependent on the speed of the field leakage out of the strip

Phase 4: Thickness measurement

  • Response from the whole strip
  • The measurement starts when the air gap signal has declined (phase 3 is included in phase 4)
  • The measurement of the whole strip corresponds to the complete energy stored in the strip, and continues until the strip response has almost declined (t3)
  • The measurement corresponds to the strip thickness
  • The resistivity does not affect the level of the whole strip response
  • The tail part after t3 is calculated with the use of the resistivity part

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