Calibration intervals for the CITS
Application Note AP8501

Polar Instruments has always maintained a policy of recommending regular maintenance and calibration to ensure that all products are performing as intended and within their published specifications. This is in common with all reputable manufacturers of professional test equipment.

The Motor Car Analogy

Every time you drive your car it does some checks at start up and all the lights go out — then you drive away. You may even check the tyres to see if one looks a little soft; hopefully you also check fluid levels occasionally.

The manufacturer recommends a service every “x” months or “y” miles. Why? To make sure all the things you cannot check (or cannot find the time to check) are OK.

If you ignore the recommended service interval you are running an increasing risk of causing damage to your vehicle, maybe having a serious accident if brakes or steering fail, or causing damage to the environment if emission controls are failing. There are many good reasons for regular maintenance. Your CITS may not have wheels but it needs maintenance just the same.

The nature of use is also significant. Using a vehicle about town in a mild climate is much less demanding than off road use in harsh conditions when servicing would be required more frequently.

CITS calibration intervals

For the CITS the calibration interval of one year is the longest time it is considered safe to wait between checks. A software reminder of this need for annual calibration is built in to help the user maintain this minimum level of maintenance. Even an instrument that is rarely used may drift over time due to temperature and humidity cycling. If the instrument is in particularly high use this period of one year may have to be reduced as replacing cables and relays will affect the measurements made. Polar Instruments would not recommend replacing a relay without recalibrating. 

Testing the range of impedance measurements

Checking regularly with the supplied semi rigid 50 ohm test line is a good practice and will show any degradation due to faulty cables or static damage. However this is only valid at 50 Ohms and the full spectrum of impedance measurements needs to be checked occasionally as mild static damage only starts to show in ways that will not be seen at 50 Ohms. Calibration is a health check for the instrument.

CITS traceability 

CITS are test and measurement instruments and are calibrated to National Standards and are therefore traceable. An instrument's traceability refers to unbroken chain of comparisons relating an instrument's measurements to a known standard. The prime object of CITS calibration, therefore, is to ensure the instrument is not just working but is producing results which can be traced to National Standards. Printouts from instruments that have exceeded their calibration interval include a warning that the test results are no longer traceable. In order to guarantee that, the equipment used for calibration must itself be regularly calibrated and a record of traceability maintained. 

Maintaining good test and calibration practices

Even the standards used to calibrate the CITS need regular checking as simply handling them and using them can cause mechanical forces which may result in changes over time. Connectors of test lines are particularly at risk and these should also be checked regularly.

The test station where the instrument is used should also be regularly checked to ensure the grounding of the electrical supply is sound and all antistatic equipment is in good condition.