Video: How to Perform a Single-point Calibration

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Janice Bennett-Livingston
Sep 29th 2015
Industrial Measurements
Life Science
Science & Sensing Technologies

If your device measures humidity, it is already drifting, and it will continue to drift because of the inherent nature of the measurement technology. So, calibration is a necessity, but how much calibration do you need? How often should your device be calibrated? What accuracy is necessary?

In order to manage costs, and because humidity affects everything in the environment, you need to set your calibration intervals to match your RH sensor's capabilities, the requirements of your process, and the demands of the environment. Using a risk-based approach to evaluate these variables will help determine your calibration needs. If your firm is risk tolerant, or your process requirements aren’t too tight, you may find that single-point field calibrations are a cost-effective solution to maintaining confidence in your sensor and understanding your environments over time.

To perform a single-point field calibration, you use a reference instrument as a standard. The major benefit is that you don't have to take the instrument out of operation. While it's fast and easy, it lacks a second point that will indicate the dynamic response of the instrument and it lacks a reliable quantification of uncertainty. Obviously not ideal in all scenarios.

So, where does the single-point field cal work? If your measured environment is stable, a single-point calibration can be a quick "sanity check" of your device. If conditions fluctuate in your environment, we recommend a multi-point calibration.


Watch the Demo - Single Point Calibration with a Handheld Meter

Here's demonstration of how to perform a single-point calibration of an HMT331 using an HM70 handheld device. NOTE – the handheld humidity device has itself been recently calibrated. Your standard needs to be accurate, otherwise, you are simply accumulating inaccuracies.

For a more in-depth discussion of Calibration methods, here is an application note: "Calibration & Adjustment of Humidity Instruments"

This note describes important items in calibration, such as:

  • Calibration Vs. Adjustment
  • Calibration Interval
  • Working Standard
  • Different types of calibration
  • Multi-Point Field Calibration One-Point In-Situ Calibration
  • Field Replaceable Sensors

Please contact us if you have questions about Vaisala Calibration products and services:

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USA 21 CFR 211.68

USA 21 CFR 211.68

Title 21 FDA Chapter I, Subchapter C - Drugs
Part 11 - Current Good Manufacturing Practice for Finished Pharmaceuticals
Subpart D - Equipment
“Equipment … shall be routinely calibrated, inspected, or checked according to a written program designed to assure proper performance. Written records of those calibration checks and inspections shall be maintained.”

USA 21 CFR 820.72

USA 21 CFR 820.72
USA Title 21 FDA Chapter I, Subchapter H - Medical Devices
Part 820 - Quality System Regulation
Subpart G - Production and Process Controls
Section 820.72 Inspection, measuring and test equipment

"(b) Calibration. Calibration procedures shall include specific directions and limits for accuracy and precision. When accuracy and precision limits are not met, there shall be provisions for remedial action to reestablish the limits and to evaluate whether there was any adverse effect on the device's quality. These activities shall be documented."

EU GMP Chapter 3.41

“Measuring, weighing, recording and control equipment should be calibrated and checked at defined intervals by appropriate methods. Adequate records of such tests should be maintained.”

EU GMP Chapter 6 6.7

EU GMP Chapter 6 6.7
"Laboratory documentation should follow the principles given in Chapter 4. An important part of this documentation deals with Quality Control and the following details should be readily available to the Quality Control Department: (...) Procedures for and records of the calibration/qualification of instruments and maintenance of equipment;..."