Cleveland Motion Controls ULTRA ISC CARTRIDGE TRANSDUCER REV AA - Manual (Page 19)

MAN-70430-0 R EV AA U LTRA S ERIES S TATIONARY S HAFT T RANSDUCER T ECHNICAL M ANUAL
3 P RODUCT A PPLICATION
The Ultra Series Cartridge Cell Transducer utilizes a twin sensing beam. Conversion from mechanical
strain to an electrical signal is accomplished using semiconductor-based, piezoresistive strain gage
elements. The full Wheatstone Bridge configuration provides an electrically balanced output yielding twice
the amount of signal swing as half-bridged transducers operated at the same excitation voltage. Integral
span compensation is used to correct for temperature induced gain changes.
Cartridge Cell Transducers can be mounted four different ways: Flange (FL), Stud (S), Pillow Block (PB)
and Bearing (BB) that incorporate their own low friction bearings. Figure 7 shows these four mounting
types. Refer to Section 4.2.2 for more information on Mounting Configurations.
MACHINE FRAME
TYPE "S"
MOUNTING
TYPE "FL"
MOUNTING
SENSING ROLL SENSING ROLL
TYPE "PB"
MOUNTING
TYPE "BR"
MOUNTING
STATIONARY/DEAD SHAFT STATIONARY/DEAD SHAFT
MACHINE FRAME
Figure 7 Cartridge Cell Transducer Mounting Types
The Ultra ISC has been developed for those customers who desire to send the transducer signal directly into
their Controller, PLC, PAC, Drive, or Local I/O. When a pair of transducers is used, the signal outputs can
be zeroed, scaled, and summed by software. It is responsibility of the customer to write this software.
3.1 Final calibration
When calibration is done though application software within the target controller, the greatest calibration
accuracy is achieved though the use of individual gain and offset parameters for each of the two transducers
(which generally are used in pairs). By using separate analog inputs in conjunction with separate gain and
offset parameters, you can correct for any transfer function differences arising from subtle mounting
variations or intrinsic to transducer output differences. If, however, the loadcells are summed first and
then digitized, the matching of loadcell outputs (as affected by such things as loadcell orientation relative to
the wrap angle) becomes more critical.
The tradeoff between hardware cost and accuracy will impact the decision as to which interfacing approach
users will decide to take.
3.2 Summing
In the majority of applications, loadcells are used in pairs. The net tension of the web must therefore be
represented by the summation of the two loadcell signals. As described above, the summation can be done
in software, so long as both analog channels can be independently observed. When only a single analog
input is available, some other form of summer is required. Two simple approaches are described below.
In the most common approach, a pair of equal-valued resistors are used in the classic resistive summer
circuit. A third resistor acts as a ground referred load which receives the combined signal from each of the
loadcells. The load resistance could be part of the analog input circuit’s input impedance, but may also be
supplemented by a fixed (external) resistance for improved load resistance stability. Often, the input
resistance to the analog input ranges from 20K ohm to 200 K ohm.
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