Industrial Controls » Reduced Calibration Costs from ROTRONIC

Reduced Calibration Costs from ROTRONIC

Many metrologists know that when it comes to humidity and temperature calibration patience…

Reduced Calibration Costs from ROTRONIC

New Airchip3000 technology from ROTRONIC reduces humidity and temperature calibration time and cost

Many metrologists know that when it comes to humidity and temperature calibration patience is a pre-requisite and any attempts at short cuts will usually result in poor data or worse…an unhappy customer. In addition there are now stringent calibration guidelines as described in cGMP’s and industry protocols such as ISO 9001, IS0/IEC 17025, & ANSI/NCSL Z540-1-1994. When a customer sends a device to be calibrated, often times, due to their own quality protocols, they will require “As Found” and “As Left” data.

“As Found” data is the recorded values of a device against a certified reference standard BEFORE any adjustments are made. “As Left” data is the recorded values of the same device AFTER calibration adjustments have been made against a certified reference standard. Before we begin it is first necessary to cover some of the common terms and definitions.

What are cGMPs?
cGMP refers to the Current Good Manufacturing Practice regulations enforced by the US Food and Drug Administration (FDA). cGMPs provide for systems that assure proper design, monitoring, and control of manufacturing processes and facilities. Adherence to the cGMP regulations assures the identity, strength, quality, and purity of drug products by requiring that manufacturers of medications adequately control manufacturing operations. This includes establishing strong quality management systems, obtaining appropriate quality raw materials, establishing robust operating procedures, detecting and investigating product quality deviations, and maintaining reliable testing laboratories. This formal system of controls at a pharmaceutical company, if adequately put into practice, helps to prevent instances of contamination, mix-ups, deviations, failures, and errors. This assures that drug products meet their quality standards.

The cGMP requirements were established to be flexible in order to allow each manufacturer to decide individually how to best implement the necessary controls by using scientifically sound design, processing methods, and testing procedures. The flexibility in these regulations allows companies to use modern technologies and innovative approaches to achieve higher quality through continual improvement.

Accordingly, the “c” in cGMP stands for “current,” requiring companies to use technologies and systems that are up-to-date in order to comply with the regulations. Systems and equipment that may have been “top-of-the-line” to prevent contamination, mix-ups, and errors 10 or 20 years ago may be less than adequate by today’s standards.

It is important to note that cGMPs are minimum requirements. Many pharmaceutical manufacturers are already implementing comprehensive, modern quality systems and risk management approaches that exceed these minimum standards.

Accuracy is a qualitative term and can be defined using an expression of the uncertainty of a measurement. For example – a pre-delivery calibration can “prove” the quoted specification of an instrument. Provided that the uncertainty of calibration is smaller than the quoted accuracy In the field of relative humidity this has sometimes been problem, however accuracy as stated in a technical specification is likely to refer to the maximum difference between a measurement taken by a reference instrument and that given by a Device Under Test (DUT).


The uncertainty of a measurement/calibration is defined as the range in which the “true value” is expected to lie. For example the DUT at a reference value of 35.0 %RH might read 34.8 %RH ± 0.7 %RH.

The uncertainty of a measurement system is calculated by tabulating the known sources of error in that system in terms of probability distributions.
Each component is then expressed in terms of equivalent probability or a standard uncertainty and combined using the equation.


The term traceability is used to refer to an unbroken chain of comparisons relating an instrument’s measurements to a known standard such as the U.S. National Institute of Standards Technology (NIST). Calibration to a traceable standard can be used to determine an instrument’s bias, precision, and accuracy. The chart below illustrates some paths for traceability:

Precision has no unit of measure and only indicates a relative degree of repeatability, i.e., how closely the values within a series of replicate measurements agree with each other. Repeatability is the result of resolution and stability.

Accuracy Vs Precision: Accuracy indicates proximity to the true value, precision to the repeatability or reproducibility of the measurement. The results of calculations or a measurement can be accurate but not precise, precise but not accurate, neither, or both. A measurement system or computational method is called valid if it is both accurate and precise.

Documentation As-found and as-left
An important gauge of good practice when documenting the value of the instrument as it was found (as-found) and how it was made (as-left) with the settings. The purpose of documenting both conditions is to make records concerning gaps or drifts during the time between instrument calibrations. If only one of these conditions will register (as-found and as-left) every time you calibrate an instrument, it will be difficult to determine how well an instrument is maintaining its calibration (accuracy) over long periods of time.

A delay or inaccuracy often is an indicator of imminent failure, which is vital for any predictive maintenance program and quality control.

Typically, the document format for the values of these conditions (as-found and as-left) is a simple table showing the calibration points or values, the ideal instrument, the current response of the instrument and the error calculated for each point. The following table is an example of what might appear on a certificate of humidity and temperature calibration with “As Left” and “As Found” data.

With the technology most metrologists use today, when a customer requests “As Found” and “As Left” data, this requires 3 FULL calibration cycles. (1) One full cycle for recording “As Found” data with no adjustments. (2) One full cycle for making the calibration adjustments. (3) One full cycle for recording the devices readings AFTER the calibration adjustments are made or “As Left” data. Then the process is repeated for the second parameter (usually humidity is adjusted after temperature). This takes an extremely long amount of time and time is money.

ROTRONIC has now introduced its advanced AIRCHIP3000 line of products and HW4 Software which, among many other features can now ELIMINATE one full calibration cycle when “As Found” and “As Left” data is requested by the customer. The new system allows for comparing a ROTRONIC transmitter connected to the HW4 software to a reference standard and storing this data in the system without making an adjustment. Several points can be saved in any order and at any time. This in its own aspect is a huge convenience. Once all the “As Found” data is recorded the reference data is still also stored in the system. Then the calibration adjustment can be done at any time automatically with the push of a button. This eliminates repeating the process for calibration adjustments (Cycle # 2 above). The picture below gives a screen shot example of the HW4 Software:

From the image you can see that both the measured values and reference values are recorded within the HW4 Software. Only when the “Adjust” button is pushed does the calibration take place. In addition the HW4 software is FDA CFR 21 part 11 and cGMP compliant with validated versions available.

By simple math you can see by eliminating one full calibration cycle you will eliminate at least 1/3 the time and cost of calibrations when “As Left” and “As Found” data is required with ROTRONIC equipment. In this day and age every bit helps.

1) The Rotronic Humidity Handbook, Copyright 2005
2) U.S. Food and Drug Administration , Device Regulation & Guidance, Post Market Requirements, Quality Regulations, Section 7 Equipment and Calibration 2009
3) Crouch , Stanley & Skoog, Douglas A. (2007) Principles of Instrumental Analysis. Pacific Grove
4) National Institute of Standards Technology, General Information


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