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Published in the Design section of Electronic Engineering Times Spectrol’s patented processes slash sensor design costs and lead times By Toni McConnel Ontario, Calif. – Design and tooling costs for high-end, multi-output custom sensors can run to several hundred thousand dollars, and lead times can range up to two years. But in two weeks Spectrol Electronics can provide prototypes of fully customized, modular sensors with analog and digital multi-function outputs, and they can do it for $1000 and no tooling charge. This impressive capability is achieved by using two Spectrol patented technologies -- digital Silver-in-Glass and analog conductive plastic -- in a sensor they call DigiSense. By combining the two technologies in a single environmentally sealed, standardized package, the DigiSense design provides thousands of output combination options. Silver-in-Glass digital logic output provides limit switch functions, logic signals, and zone logic. The conductive-plastic potentiometric output furnishes the analog signal and absolute position, can survive 300 million dither cycles, and offers custom functions. The analog and digital circuits are completely isolated, providing redundant signal capability in the same package. Seven terminals can be configured as input, output or ground. The customer has complete design flexibility in terms of the analog resistive angle and slope and the position of the logic points. According to Spectrol, DigiSense is virtually immune to damage and is able to operate reliably in severe environments. Mean-time-between-failure (MTBF) exceeds 2 million cycles. The Silver-in-Glass process involves the deposition of a smooth thick-film glass over the entire surface of an alumina ceramic substrate. After the glass layer has been fused to the substrate, a conductor pattern of palladium silver is printed on top of the glass. During kiln firing, the silver conductor sinks into the glass surface, forming a very smooth switching surface. Thick-film Silver-in-Glass material technology adds physical strength to the sensor design and minimizes the step height differential between the conductor and insulator surface. For example, designs utilizing a composite board with copper foil etching typically have a bum-up contact intersection on the order of 23 to 35 microns. For Silver-in-Glass, the contacts must only climb up between 4 to 6 microns at each contact point as the shaft is rotated. The relatively flat, smooth wiping surface helps eliminate wear, electrical noise, and dimensional instability that can cause switching accuracy failures. Sensors utilizing this technology typically have a 10 mA current capacity and a rotational life exceeding 25 million switch cycles. Switches with a single track carrying 100 mA have been produced. Spectrol's multi-fingered, precious-metal, hoe-shaped contacts ensure the maintenance of constant pressure against the thick-film element in spite of wear, vibration, and shock, enhancing accuracy and eliminating problems associated with contact bounce. Conductive plastic technology was initially designed for use with Spectrol's exhaust-gas-recirculation valve-position sensor (EVP). The technology, formulated to survive the 300 million dither cycles -- which was Ford Motor Company's benchmark -- is also used on other Spectrol automotive sensors, such as a pedal position and "drive-by-wire" sensors. The resistive element is a conductive plastic polymer, screened and kiln fired. Temperature range is –40 degrees C to 150 degrees C. The process provides an output signal that is very smooth, exhibits extremely low noise, and has virtually infinite resolution. A multi-output device, the DigiSense sensor can be used as an actuator (on a control panel) for pedal position sensing, industrial controls, throttle position sensing, or motor actuators, or as a feedback position sensor (on a pivot point feeding back a position) for angular motion sensing or pivot point position feedback. In most closed-loop control circuits, there are both actuator and feedback devices. The actuator is adjusted by hand (pedals, throttles, levers, panel controls, joysticks) and sets the speed, height and position of a given mechanical action. The actuator sends a voltage signal to a controller, which starts the mechanical action. The feedback sensor transduces a mechanical angle into a voltage signal which closes the control loop. The mechanical angle changes until the feedback sensor sends the right voltage back to the controller. Spectrol’s technology allows the removal of external limits switches, microswitches, wire harnessing, along with their associated assembly labor costs. DigiSense will also improve switching accuracy and eliminate components in a feedback sensing system, thereby reducing the component count and increasing overall reliability. In some cases, DigiSense will replace two potentiometers, two to four microswitches, and mechanical gears and cams. Because of its redundant functions, the sensor increases the margin of safety. DigiSense design utilizes a standard housing, bushing, shaft, and pin configuration. The heart of the sensor, which is the element, is the key customer-defined variable. Engineers can design their own element to match their required functions, then fax the form directly to Spectrol Electronics. A round shaft is standard. D-shaped, double D-shaped and shaft slots are options. The electrical angle (analog output) has a maximum of 160 degrees when using a single slope. If a forward and reverse function is desired, the maximum angle is +/- 80 degrees. Logic switch points are entirely customer-defined within an angle of 160 degrees. Up to four logic points are available if there is only one Vin. The DigiSense sensor can be used in diverse applications including material handling equipment such as forklifts, personnel carriers (throttle position), agricultural tractors, industrial controls (joysticks), marine applications (throttle position sensors) and motor controller actuators. Back to Word Sculptors main page
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