Absolute Voltage Calibration.

Hum Measurement.

18. Frequency Calibration.

These instruments are tested groups of five, that is, each test is performed on each instrument of the group before the test man proceeds to the next

Figure 2. Calibrating a Type 722 Precision Condenser in the Standardizing Laboratory.

test. In this way, more efficient use of time and equipment is possible than when the complete test schedule is performed on each instrument in turn. Yet the minimum test time per instrument is about six man hours, when no difficulties that require trouble shooting are encountered.

The activities of the Standardizing Laboratory, however, are not confined to production alone, but also touch engineering, sales, and service.

The engineering functions of the laboratory are threefold, embracing the determination of performance data on new instruments, the maintenance of standards, and the training of engineering assistants for the development engineering group.

Trial production lots of new instruments (usually numbering either five or ten units) are given particularly comprehensive tests. Over-all performance tests are made to determine catalog specifications; errors and omissions in manufac experimenter

Figure 3. Modulation tests on a Type 605 Standard-Signal Generator.

turing specifications are corrected; and, finally, operating tests under severe temperature and humidity conditions are made.

In order to calibrate instruments for voltage, resistance, capacitance, inductance, and frequency, accurate standards are necessary. These are maintained in the laboratory with the exception of the Primary Standard of Frequency, which i^located in the Engineering Department. All working standards of resistance, inductance, and capacitance are intercompared periodically, and several are sent yearly to the U. S. Bureau of Standards for recalibration.

Testing specifications allow in general about three-quarters of the tolerance given in the catalog specifications. That is, a resistor with a published accuracy of 0.1% is rejected by the laboratory if its error is over 0.075%.

The Standardizing Laboratory provides excellent training for engineering assistants, and, from time to time, laboratory personnel are assigned to the development engineering group for work under the supervision of development engineers.

Not so obvious, but extremely important is the laboratory's connection with sales. It is the responsibility of the laboratory administration to control inventories so that no more than four months' supply of major instruments is kept in the stockroom. This policy lias two beneficial results. It permits laboratory time to be allotted most efficiently in terms of salable instruments, and it assures the customer that the calibration of any instrument that he purchases is no more than four months old. Some particularly critical calibrations, however, are made only upon receipt of a customer's order.

Each repaired instrument is completely tested and calibrated to the same specifications as a new instrument of the same type. Since the volume of repairs cannot be easily controlled, close cooperation between the laboratory and the Service Department is essential in order to avoid delays in returning repaired instruments to their owners.

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