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Importance Of Calibration For T&M Instruments
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The impact of even a small error in measurement can be tremendous in terms of loss in revenue. Hence, even the smallest of errors in delivery (data accuracy) is unacceptable due to the vast sums of money involved, first, when manufacturers buy instruments, and later when prototypes go into production. Thus, it has become vital to have the equipment calibrated on time.
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Saturday, May 19, 2012:
Calibration is the process of configuring an instrument to provide a result for a sample within an acceptable range. To ensure that electronics test equipment performs as per specifications, it is necessary that it receives its periodic calibration. Over a period of time, every device experiences physical stress or variations that cause a decline in its performance levels. Hence, calibration is the key to accurate data. Calibration can be of two types—the first is soft calibration, which is done on the basis of internal signals and software algorithm routines. While hard calibration is done once in a year or two, using industry standard signal generators.
While calibrating, the procedure may vary from product to product. However, this process generally involves using the instrument to test samples of one or more known values called calibrators.
With technological advancements, several instruments like oscilloscopes today provide state of the art design and debug solutions and come with an inbuilt calibrator. Thus, oscilloscopes offer extensive triggers to identify elusive anomalies. However, once they are connected to active probes, calibration is required so as to detect and capture the signal accurately. Agilent offers the widest range of application and customer support locally. Local customer support centre holds an ISO 9002 certification and is an NABL accredited calibration centre. “We offer a very unique web based customer interface to all our serviced install base and a unique offering of onsite calibration called VOSCAL (volume onsite calibration). We also provide calibration and adjustment software for those customers who have the hardware capabilities in-house. These are the same OEM calibration software used in Agilent service centres,” informs Sadaf Arif Siddiqui, technical marketing specialist, Agilent Technologies Pvt Ltd.
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How frequently should calibration be done?
It is difficult to specify the time intervals between calibration. A daily testing control solution of known values can provide a quantitative indication of the instrument’s performance, which can be recorded. If the control data indicates that the instrument’s performance is stable, or is varying randomly but well within the acceptable range of values, then there is no need to recalibrate the instrument. However, if the historical data indicates a trend beyond the limit of the acceptable range, then recalibration is warranted. Informs Nasser Salim Jariwala, head, business development and regional manager, west India, Rhode & Schwarz, “There is no special maintenance required other than the usual procedure followed for test and measurement (T&M) products. We at Rohde & Schwarz recommend calibration of a unit after one year of its operation. Also, all prominent manufacturers have their own calibration facilities in their labs.”
What players offer
Normally, specific adjusters are required to enable the instrument to be calibrated. Additionally, the required test setup and suitable test equipment to perform the calibration procedure is required. Shares Kumaraswamy ML, deputy general manager, TMI and Communications products division, Yokogawa India Ltd, “Scopes usually require periodic maintenance for healthy operations related to its published specifications. Hence, not only do companies offer calibration services for their devices but they also have dedicated service and repair centres to take care of periodic maintenance and repair.”
Says Praveen Kumar Gupta, director, Avante Global Services Pvt Ltd, “An oscilloscope calibrator is an independent device that offers very high accuracy and can be calibrated. These are being offered by a select few calibration equipment manufacturers only. Most manufacturers recognise the need to maintain properly calibrated devices for high accuracy measurements. To help meet calibration needs, manufacturers provide calibration support and services that include manual calibration procedures, services to calibrate products and automated calibration software.”
Adds Nandini Subramanya, marketing communications manager, National Instruments (NI) India, “Every PXI-5922 is factory calibrated to verify that it meets NIST-traceable standards. It has an onboard calibration circuit that corrects it for environmental effects on linearity, gain, offset and input bias current. Also, users can perform self calibration to ensure that the board is within specifications.” With ISO 17025 accredited calibration, NI offers traceable and complaint calibration services to its clients. With traceable calibration, users can track how instruments are performing as well as minimise the time and costs associated with unscheduled downtime and quality issues.
The RTO 1044 series of oscilloscopes offered by Rhode and Schwarz have self-test and self-alignment features. Self-alignment involves performing horizontal and vertical alignment, ideally, 0.5 hours after the power is on. If self-alignment fails, the ‘UNCAL’ flag appears on the screen indicating that calibration has not been processed. Adds Nasser Salim Jariwala, “Both self-testing and self-alignment can be initiated by the customer at any time during the operation of the unit. We are equipped to repair and calibrate these scopes in the event of failure. We have trained service experts and have a NABL-certified lab in Bengaluru.”
While manufacturers do offer calibration facilities, it is the users who have to ensure that the equipment is operating as per specifications. This is achieved by rigorously maintaining a process whereby all the equipment in use is calibrated. This will ensure that all the measurements are accurately made and with sufficient records, any test equipment problem can be traced and rectified.
-- Richa Chakravarty
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