Calibration is never optional. That's what Dickson Co., an Addison, Ill.-based maker of chart recorders, dataloggers and other instruments, asserts on its site, where it cautions end-users on the importance of calibration.

"Whatever situations compel you to control temperature, humidity, pressure or other conditions, also require you to calibrate the dataloggers or chart recorders used to monitor those conditions," the site cautions.

Here are Dickson's guidelines.
  • Don't Expect Lifetime Accuracy. All instruments lose accuracy over time due to normal use and the environmental conditions to which they are exposed. Periodic NIST-certified calibrations maintain the accuracy of dataloggers and chart recorders throughout their lives.

  • Check for Quality Control. Periodic calibration checks that include both before- and after-calibration data are the only way to ensure that measuring instruments are accurate and allow users to identify out-of-tolerance conditions. "Before data," also called "as received data," refers to the readings provided by a datalogger or chart recorder before it is recalibrated and returned to original operating specifications. Once your instrument is recalibrated, you cannot retroactively obtain "before" data. "As received" or "before data" is needed for any application requiring data on out-of-tolerance conditions.

  • Remember Regulatory Compliance. A wide range of regulations require strict adherence to regular calibration schedules and documentation of data logger and chart recorder measurement accuracy.

  • Limit Liability Concerns. Standard operating procedures that demonstrate due diligence in adhering to calibration schedules and documented proof (including both before- and after-calibration data) help protect against liability claims.
If you're not sure how often to calibrate, Dickson addresses that question on its site with three steps.
  • Step 1: First Calibration Checkup. For most applications, the recommended first-time interval for calibration is every six months. This first calibration should include before-calibration data (N450 Compliance-Max or N550 Before and After).

  • Step 2: Stretch the Interval. If the "before" data is acceptable, stretch the calibration interval. In other words, if the before-calibration data shows that operation was acceptably close to the stated accuracy of the instrument, you can lengthen the interval to, for example, seven months. Remember to include before-calibration data (N450 Compliance-Max or N550 Before and After).

  • Step 3: Revert to the Previous Interval if "Before" Data is Unacceptable. If before-calibration data reveals that the device stayed acceptably close to the stated accuracy of the instrument, then you can continue to stretch the intervals between calibrations. Eventually, you will find the time period that does have significant effect on the accuracy of your unit. When you reach that point, go back to the prior calibration interval. This calibration schedule should be adhered to for the life of your datalogger or chart recorder when used in the same application.