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| Application Stories IR THERMOMETER
CALIBRATION This article provides an overall review of different types of infrared calibration sources (Blackbody Sources) and how to use them to calibrate infrared products. There are basically two types of infrared calibration sources, Hot Plate Blackbody source and Cavity type blackbody source. The hot plate style consists of a metal plate (usually aluminum) with or without concentric grooves where the temperature of the plate is set and controlled using either an inexpensive potentiometer dial or a high-end temperature controller. The temperature of the plate is sensed using either a thermocouple or an RTD probe. The hot plate is usually painted dull black to improve the surface emissivity. The surface emissivity of a hot plate calibration source is typically 0.95. Figure 1 shows a very basic hot plate blackbody source with a potentiometer dial (OMEGA's model BB-2A). Figure 2 shows a high-end plate blackbody source with a built-in temperature controller (OMEGA's model BB704). The calibration source with built-in temperature controller has much better accuracy and stability compared to a potentiometer dial type unit. The cavity type blackbody source consists of a blind hole in a cylinder or a sphere where the temperature of the cavity is controlled by a temperature controller, using a thermocouple probe. The cavity type blackbody source has a higher surface emissivity than a hot plate blackbody unit. The emissivity of a cavity type blackbody source is typically 0.98 or higher. Figure 3 shows a cavity type blackbody source with a built-in temperature controller (OMEGA's model BB705). The cavity type blackbodies typically go to higher temperatures (over 1000°F) than hot plate blackbodies. In addition, having a higher emissivity value makes them ideal for precise calibration tasks. In order to calibrate an infrared thermometer, a blackbody calibration source is required. There are three factors to consider when selecting a blackbody calibration source:
1 Type of blackbody (Hot Plate or
Cavity type) tells us about the construction and 2 Target area tell us how large of an area we can check our infrared thermometers with. The target area should be larger than the field of view of the thermometer; otherwise the infrared thermometer will be measuring the target area plus some of the surrounding cooler areas. Normally, an infrared thermometer is checked against a blackbody source at a relatively close distance (about 0.5 to 3 feet depending on the taget area). 3 The higher the target emissivity, the more ideal is the calibration. At lower emissivity targets, wavelength bandwidth of the infrared thermometer comes into play. Ideally at E=1.00, wavelength bandwidth of the DUT (Device Under Test) is not a factor. When using a blackbody calibration source, we need to follow certain ground rules: * The infrared thermometer should be aimed
perpendicular to the target area of the blackbody unit. If aimed at an
angle, reflected IR * The field of view area of the thermometer at a selected distance should be smaller than the target area of the blackbox unit. * Do not bring the infrared thermometer too close to the target area of the blackbody especially at high temperatures. The radiated heat from the blackbody can not only impair calibration accuracy but also potentially damage the unit under test. * Always aim the infrared thermometer to the center of the target area.
* Do not unplug a blackbody calibration source while it is hot. There are usually built-in fans to remove the heat even when the power switch is off. Let the internal fan continue to run until the unit is cooled down. We hope this article has provided some useful information on how to select a blackbody calibration source and how to use them properly in the field. OMEGA TOOLING SHOP CATCHES
ERRORS Part rework wastes man-hours and reduces spindle in-cut time, greatly hamstringing a shop's productivity no matter what the part is. The solution for a Boeing tool shop, manufacturer of assembly jigs and fixtures for complex aerospace components, was to verify its CNC machines prior to the process, instead of relying on CMMs for an after-the-fact check against the machines. Proven in advance through Renishaw ML10 Laser calibration and QC10 Ballbar diagnoses, the machines can be trusted to produce parts - no matter how complex or critical - that will meet spec before removal from the machine.
The shop's first step was to baseline its machines through ballbar and laser testing, measuring the accuracies of each and flagging those in need of maintenance. The second step is to fingerprint each healthy machine over time with periodic tests. By monitoring how each machine's positioning and contouring capabilities are trending, the shop avoids putting a fine-toleranced job on a "loose" machine. In the past, the tooling shop used the circle-diamond-square test which was helpful in finding errors in the X-Y plane, but often missed errors in the X-Z and Y-Z planes. Subsequent ballbar diagnosis on a five-axis machine that passed the circle-diamond-square test revealed following errors as large as 0.065", a result of misalignment between rotary and linear axes. The ballbar and laser tools complement each other and even use the same notebook PC for machine evaluation. The QC10 Ballbar measures and plots dynamic, multi-axis errors that are only apparent when the machine is in motion. It tracks machine movement to ±0.5 micron, allowing calculation of circularity error, servo gain mismatch, vibration, stick-slip errors, backlash, repeatability and scale mismatch, as well as machine geometry. Accompanying diagnostic software calculates error weights and values and converts the ballbar data into a polar plot of the machine's true movement. The ML10 Laser performs straightness, linearity, angularity, squareness and parallelism data capture to detect backlash, scaling errors and general component wear. The system is capable of measurement to ±1.1 ppm accuracy. The tooling shop has since eliminated part rework on machines it has fingerprinted. "With fingerprinting, we know immediately when a machine's capabilities decline, meaning we can correct the problem and return the machine to its original performance level," said a company official. Renishaw, Inc. SOLVENT RECOVERY SYSTEMS Environmental consciousness is dictated by law and personal awareness. Young and old alike are taught by legal fiat or their conscious that you just don't dump your trash anywhere, especially if it contains a potentially hazardous material. Needless to say, industry operates under even stricter rules. While use of many hazardous solvents are banned altogether, there are still hundreds of liquids and solvents without which industry could not function. Recovery of these is both practical and economical. The question of how you separate the solvent from the solute is one that has been solved by a company called S.R.S. Environment, Inc. in Saint-Nicolas, Quebec. The company manufactures a series of five different solvent recovery systems that distill and condense solvents, thinners and cleaners from a wide range of industrial liquids and solutions. The five models range in capacity from 3.5 to 55 gallons (13 to 208L). Operation of the microprocessor-controlled distillation system is simplicity itself. After pouring in the liquid or solution to be distilled, the operator secures the lid fitted with four De-Sta-Co vertical hold-down toggle clamps. Vertical hold-down action toggle clamps are identified by their vertical handles. These clamps are manufactured with a range of holding capacities up to 6,000 lb (2,727 kg). The hold-down bar, also called the clamping bar, exhibits a minimum of 90 degrees opening angle and can be solid or U-shaped. The base is straight or flange-mounted (standard version). It is the toggle action that is the key to proper closure of the S.R.S. equipment. Toggle action clamps operate through a linkage system of levers and pivots. The fixed-length levers, connected by pivot pins, supply the action and clamping force. In toggle action there is an over-center lock point which is a fixed stop and linkage. Once in the over-center position, the clamp cannot move or unlock unless the linkage is moved. All types of toggle clamps have this same action, just oriented differently. S.R.S. manufactures five different solvent recovery systems that use two different De-Sta-Co toggle clamps. Four of these units use the model 518 and one uses the model 210-U. For the S.R.S. equipment, the standard or flange mounted clamps are specified. The model 518 features a forged hold-down bar and ergonomic plastic grip. This clamp has a holding capacity of 500 lb (227 kg). One of the major features of this clamp is the greater clearance under the bar. Due to the bar design, this is twice the normal clearance in this size clamp. The model 210-U, used on the company's largest solvent recovery system, is one of De-Sta-Co's most widely used clamps. The clamp is available in eight different sizes with the U-model having a holding capacity of 600 lb (272 kg). Like the model 518, it features an ergonomic grip on a vertical handle. De-Sta-Co Industries SLOT MACHINE Brandt Engineered Products Ltd. of Regina, Saskatchewan has designed and built a self powered slot machine (SPS). This machine is used to maintain rail beds across North America.
The operator of the back hoe, while seated in the cab of the excavator, uses a radio remote control system to move the consist to exactly the position required for him to perform the maintenance work. "Having everything accessible at the
job site really speeds up every job," says Georgetown president Steve
Orrell, "and the remote control is a big Barry Burt, project engineer at Bradt, says, "we looked at a number of radio remote control systems to run the operation of the slot machine. We decided on the Cattron-Theimeg MP96 RCL because of its sturdiness and its many diagnostic and safety features. After testing one unit, we were very impressed with its operation. As a result, we've purchased additional Cattron-Theimeg systems for the SPS units." The Cattron-Theimeg MP96 RCL, designed
specifically for use on rail car movers and locomotives, is a
microprocessor-based remote control The radio remote transmitter, mounted in the excavator cab, can precisely control the engine's throttle and brakes, allowing the excavator operator to easily position the machine from a safe and convenient vantage point. Self-Powered Slot Machines, designed by Brandt Engineered Products for Georgetown Rail Equipment Company, are currently being used across Canada, the United States and Mexico. Cattron-Theimeg Canada Limited Canadian Industrial Equipment News November 2003
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overall performance of the unit.
energy can impair calibration accuracy.
*
When changing the temperature setpoint on the blackbody unit, make sure
the unit is fully stabilized to the new temperature setting before making
any calibration tests. Usually going up in temperature takes less time
than going down in temperature.
"A
CMM can tell us only when there is an error on the part, but not if there
is a repeatable error traceable to the machine tool," said a company
official.
Commissioned
by Georgetown Rail Equipment Company of Georgetown, Texas, the SPS
consists of an engine and four attached rail cars. The cars carry gravel,
ties and rails and an on-board