A set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realised by standards. The result of a calibration permits either the assignment of values of measurement to the indications or the determination of corrections with respect to indications. The result of a calibration may be recorded in a document called a calibration certification or a calibration report.


The United Kingdom Accreditation Service is the sole national accreditation body recognised by government, against internationally agreed standards, organisations that provide certification, testing, inspection and calibration services. Accreditation by UKAS demonstrates the competence, impartiality and performance capability of these evaluators.

UKAS Certification

A Certificate of Calibration produced by a accredited UKAS company, using UKAS calibrated test instrumentation by engineers who are trained to calibrated in the quality and procedures agreed by UKAS.

Traceable Certification

A certificate that is produced using test equipment calibrated by a UKAS Accredited company. This does not in any way make it a UKAS certificate as the company carrying out the Calibration is not UKAS accredited, therefore not auditing in their methods and procedures.


Accreditation is a formal, third party recognition of competence to perform specific tasks. It provides a means to identify a proven, competent evaluator so that the selection of a laboratory, inspection or certification body is an informed choice.

ISO 9001:2008

ISO means, the International Organisation for Standardisation. The quality policy is a formal statement from management, closely linked to the business plan and to customer needs. The quality policy is understood and followed at all levels and by all employees. Each employee works towards measurable objectives.

ISO 17025:2005

ISO 17025:2005 for Calibration & Testing Laboratories is the General Requirements for the Competence of Calibration and Testing Laboratories. There are many commonalities with the ISO 9001 standard, but ISO/IEC 17025 adds in the concept of competence to the equation. And it applies directly to those organizations that produce testing and calibration results. This International Standard covers technical competence requirements that are not covered by the Quality Management standard ISO 9001:2008.


The term measurement traceability is used to refer to an unbroken chain of comparisons relating an instrument's measurements to a known standard. Calibration to a traceable standard can be used to determine an instrument's bias, precision, and accuracy.


Uncertainty of measurement is the doubt that exists about the result of any measurement.

Every measurement, even the most careful, always has a margin of doubt. In everyday speech, this might be expressed as 'give or take' ... e.g. a table might be two metres long 'give or take a centimetre'.

Measured Error

Error is the difference between the measured value and the 'true value' of the thing being measured. Errors are not the same as uncertainties (even though it has been common in the past to use the words interchangeably in phrases like 'error analysis').


The closeness of the agreement between measurement result and true value. (Accuracy is a qualitative term only.) Accuracy (or rather inaccuracy) is not the same as uncertainty. Unfortunately, usage of these words is often confused. Correctly speaking, 'accuracy' is a qualitative term (e.g. you could say that a measurement was 'accurate' or 'not accurate'). Uncertainty is quantitative. When a 'plus or minus' figure is quoted, it may be called an uncertainty, but not an accuracy.


When repeated measurements give different results, we want to know how widely spread the readings are. The spread of values tells us something about the uncertainty of a measurement. By knowing how large this spread is, we can begin to judge the quality of the measurement or the set of measurements.


The Aerospace Material Specification AMS2750D covers pyrometric requirements for thermal processing equipment used for heat treatment. It covers temperature sensors, instrumentation, thermal processing equipment systems accuracy tests and temperature uniformity surveys. Adherence to the specification is necessary to ensure that parts or raw materials are heat treated in accordance with the applicable specifications. Roxspur provide two types of instrumentation, which meet the requirements of thermal processing equipment as defined in the specification.

1) Field Test Instrumentation and 2) Controlling Monitoring or Recording Instrumentation

Temperature Uniformity Survey (TUS)

This is a service that is offered to see how a Thermal unit can distribute its heat. Thermocouples are placed in various positions and a put under a certain temperature condition. It is how close together the readings of these thermocouples that determines how uniform the unit is. These tests are usually ran on ovens, fridges, furnaces and kilns.

System Accuracy Tests (SAT)

The purpose of the SAT associated with Instrumentation is to provide an authenticated record of the instrument accuracy within a defined level of tolerance difference through a chain of traceability to NIST or equivalent National reference standard. These are performed on the temperature control and recording systems in each control zone of each piece of thermal processing equipment that is used for production heat treatments.

Methods Of Calibration

There are numerous ways to calibrate a instrument. From injecting a signal to removing an instrument and putting it into a known heat source. Below is a list and explanation of the different types:-

  • Electrical simulation: Calibrated Electrical standard is used to output a known electrical value (V, A or ), a reading is taken from the unit under test and both values are compared.
  • Electrical measure: Output signal from the unit under test is inputted in to an electrical standard and both values are compared.
  • Thermal Comparison: Readings from Temperature sensor under test and calibrated sensor are taken at a temperature and both values are compared.
  • Pressure Comparison: Calibrated pressure sensor is used to apply known rising and falling pressure values, rising and falling readings are taken from the pressure sensor under test and both values are compared.
  • Temperature Uniformity Survey: Calibrated thermocouples are inserted in to the oven at set positions, the oven is set at specific temperature points and the values from the thermocouples are recorded.
  • Timers: Both a calibrated stop watch and the unit under test are started at the same time, after the required time both timers are stopped at the same time and both values are compared.
  • Flow: Unit under test is set to a flow level and air flow is started, a timer is used to record the time taken for a set volume of air to pass through the flow meter, results are then calculated.
  • Infrared: Unit under test is sited in to a furnace set at a known temperature; readings are taken and compared to a calibrated standard.
  • Disappearing filament Pyrometer: Unit is sited against a calibrated Filament bulb set at a known temperature; rising and falling results are taken and compared to the results for our bulb.