Automate and calibrate
Using an automated procedure, one company cut its calibration time, reducing the amount of time an instrument is out of service.
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 12/1/2004 2:00:00 AM
DEVICE UNDER TEST
RF signal generators made by Agilent Technologies, IFR Systems, and Rohde & Schwarz—a total of 28 models. The instruments, which cover the frequency range from 100 kHz to 18 GHz, require periodic calibration to their published specifications.
THE CHALLENGE
Develop automated stations to fully calibrate the RF signal generators. Reduce the time a technician spends on a calibration and reduce the time the signal generators are out of service. Build two stations, one for an engineering facility in Atlanta and another for a manufacturing facility in Mexico. Both stations must calibrate hundreds of signal generators per year and must be able to download calibration procedures over a network.
THE TOOLS
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Agilent Technologies: measuring receiver, signal generator, microwave converter, audio analyzer, sensor module, spectrum analyzer, and RF power meter with sensors. www.tm.agilent.com.
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Fluke: metrology software. www.fluke.com.
PROJECT DESCRIPTION
Scientific Atlanta develops and manufactures video equipment for the broadcast and consumer markets. Engineers develop new products at the company headquarters in Atlanta, GA, and at a facility in Naperville, IL. Manufacturing takes place in Naperville and in Juarez, Mexico.
To test the company's products, engineers and technicians use RF signal generators that require periodic calibration. To cut calibration time, metrologists at the company's Atlanta calibration lab developed automated calibration stations under the direction of lab manager Tom Harris.
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| Automated calibration stations reduce test time for RF signal generators by two-thirds over manual calibrations. |
Each station (see figure) uses several calibration standards in a suite of tests that include harmonic distortion, frequency accuracy, AM/FM accuracy, modulation distortion, residual AM/FM, RF output level accuracy, and flatness. Using Fluke's Met/Cal software, engineers developed automated calibration procedures to control the UUT and the calibration equipment. They purchased additional procedures from third-party developers.
The metrologists in Atlanta also developed a database that stores calibration records and tracks the signal generators. Thus, technicians, including senior calibration technician Steve Reeves, can ensure that each generator returns to the cal lab at the right interval. Most of the signal generators are on annual calibration cycles, but if an instrument returns to the lab out of tolerance, its calibration cycle will shorten.
Each year, the calibration station based in the Atlanta office travels to Naperville for two weeks where technicians calibrate that facility's RF signal generators. Because all calibration procedures are stored on a server in Atlanta, technicians in both Naperville and Juarez must download their procedures over the company network.
To calibrate an RF signal generator, a technician must connect a series of calibration standards to the instrument and perform the specified procedure. The calibration software guides the technician through each procedure and provides prompts that indicate when it is time to change the setup. Where technicians once performed manual calculations to determine if a signal generator met specifications for properties such as modulation distortion, software now performs this task automatically.
Engineers and technicians use the stations to store calibration data for printing or analysis. Besides test results, the data includes technician names, environmental conditions, standards used, calibration date, and due date. Following each calibration, the station prints a calibration label that includes the date of the instrument's next appointment at the cal lab.
RESULTS
The automated calibration stations significantly reduce the time it takes the engineers to calibrate each signal generator. Previously, manual calibration of most RF signal generators would take 3 hrs or more. The automated procedure performs the task in 1 hr or less, which reduces the time that an instrument is out of service. Currently, 60% to 65% of instruments calibrated in Atlanta and 70% to 78% of instruments calibrated in Juarez return to use within 1 day.
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