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Partnering September, 2017
Using Adaptive Digital Signal Conditioners in Manufacturing
By Will Meenan, Kaman Precision Products M
ore manufacturers than ever are requiring sensors for condition monitoring in their
machines and processes. New digital signal conditioner technology is now available that simplifies the use of eddy current (inductive) displace- ment sensors for high precision/high reliability applications. This technol- ogy is an excellent option for moni- toring movement, position, vibration, alignment, or deflection, especially where parts operate in high temper- atures or within environmental con- taminants. Unlike previous versions that required circuit modifications and manual calibration to match the required target, sensor, cable length, and range, these digital signal condi- tioners configure themselves in a matter of minutes. In addition, the technology works with a wide variety of sensors.
Types of Sensors Many sensor options are avail-
able for machine condition monitor- ing, including inductive technology, linear variable differential trans- formers (LVDTs), laser triangula- tion, capacitive, and ultrasonic sys- tems, as well air gauging, Hall ef- fect, and optical systems. Each tech- nology has distinct advantages and disadvantages, depending on the ap- plication. Eddy current sensors are gener-
ally much more insensitive to envi- ronmental contaminants than other options. They operate on the princi- ple of impedance variation caused by eddy currents induced in a conduc- tive target by a sensor coil. The sen- sor coil is excited by a high frequen- cy oscillator, which generates an electromagnetic field that couples
with the target. Signal conditioning electronics sense impedance varia- tion as the gap between sensor and target changes and translates it into a usable displacement signal. This technology provides extremely high (sub-microinch) resolution. Eddy current sensors can “see
through” non-conductive materials, making these sensors useful in such applications as paint, rubber, and paper thickness. They can also be a good option for operation over a wide variety of temperatures and environ- ments, including dust, oil, gas, diesel fuel, liquid oxygen, and rocket fuel. Inductive technology is used in
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many high-performance sensor ap- plications, especially those that re- quire higher frequency responses in challenging environments and tem- peratures. They allow operators to monitor a machine and determine when it has to be taken offline for maintenance. Conversely, the sen- sor may indicate that the machine is running well, and that mainte- nance is not required. If, for exam- ple, the machine in question is a crucial pump operating in an inac- cessible location, precise informa- tion on machine condition can be critical to a company’s bottom line. High-precision inductive sen-
sors can also be used to monitor or control the quality of a process. The sensors provide a real-time control signal to the machine or a display to the operators so they can adjust ma- chine performance.
Digital Signal Conditioning Previous signal conditioner tech-
nology required hardware or software configuration to accommodate differ- ent sensors, target materials, cable lengths, and range. This was more costly and time-consuming to set up. New digital signal processors, includ- ing digiVIT from Kaman, simplify the use of eddy current sensors for high performance applications. Calibration is performed by
menu options and pushbuttons on the front panel, as opposed to adjust- ment of analog potentiometers. Re- configuration, if required, can be per- formed in a matter of minutes. A highly-linear output signal is achieved internally using digital lin- earization techniques. Temperature compensation of the output signal, desirable to minimize measurement temperature effects, is performed by the internal microprocessor and can be easily set up by the user, in many cases in situ. The digiVIT signal con- ditioner also includes user-program- mable functions, such as:
l l
Relay set points for indication of out-of-tolerance conditions or process control.
Digital low-pass filtering to improve resolution.
l Adjustable sensor sample rate. l
Quick two-point adjustment rather than full calibration when replacing broken sensors.
Kaman’s digiVIT has been used
in a range of manufacturing environ- ments. In one metal stamping process, the customer’s feed stock had to be checked for straightness and flatness. The metal type was changed several times a day. Eddy current technology was ideal for the oily machine environment, but re- quired recalibration for each differ- ent type of metal, which was too time-consuming. With the digiVIT, recalibration took only a matter of
New digital signal conditioner technology is now available
that simplifies the use of eddy current (inductive)
displacement sensors for high precision/high reliability applications.
minutes, making the measurement practical. For another user with many
large assembly machines, monthly sensor calibration was required for quality control purposes. The sensors were located far from the signal con- ditioner making calibration of analog sensors difficult and time-consum- ing. Replacing the analog systems with a digiVIT signal conditioner re- quired only a two-point calibration adjustment, reducing calibration time significantly. Finally, one customer combined
the digiVIT with a laser for a paper thickness measuring application. This customer performed a special calibration over a limited range to optimize resolution. Digital filtering and in situ temperature compensa- tion were enabled to further improve performance. The digiVIT turned out to be easy to implement. The new digital signal condi-
tioner allows users to easily work with a wide variety of measuring sys- tem configurations and operating conditions. For applications where high performance is a must, the new digital signal conditioner technology
is an attractive option. Contact: Kaman Precision Prod-
ucts, 217 Smith Street, Middletown, CT 06457 % 860-632-4536 Web:
www.kaman.com r
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