How often should you calibrate your CITS?

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 recommends recalibrating the CITS when a relay is replaced.

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.