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Muffle furnace · Calibration procedure

Temperature accuracy

Compares the furnace display with a calibrated reference thermocouple placed in the working zone at the set points used in testing.

Photo of a Muffle furnace
Photo: Karelj, Public domain (cropped), via Wikimedia Commons
PURPOSE

Why this is checked

Sulphated ash and ignition tests specify a temperature, such as 600 ± 50 °C. The furnace must actually reach that temperature where crucibles sit.

Frequency

Typically every 6 months, and after element or thermocouple replacement, as defined in your SOP.

Learn how the Muffle furnace works
YOU WILL NEED

Standards & tools

  • Calibrated reference thermocouple (type K or N) with a calibrated indicator, traceable to national standards
BEFORE YOU START

Prerequisites

  • Chamber empty and clean
  • Reference probe positioned in the centre of the working zone through the vent or door port
PROCEDURE

Step by step

  1. 1Place the reference thermocouple tip in the centre of the chamber.
  2. 2Set the furnace to the first set point (for example 450 °C) and allow it to stabilise for at least 30 minutes.
  3. 3Record the furnace display and reference reading several times over a few minutes.
  4. 4Repeat at the other set points (for example 600 °C and 800 °C).
RECORD

Example observation table

Set point (°C)Display (°C)Reference (°C)Difference (°C)
450450446.8−3.2
600600604.5+4.5
800800793.9−6.1
CALCULATION

How to calculate the result

Difference = Reference reading − Display reading
  1. At 600 °C: 604.5 − 600 = +4.5 °C
ACCEPTANCE CRITERIA

Pass if

  • Difference within the limit in your SOP (commonly ±10 °C), and always well inside the method tolerance, for example 600 ± 50 °C.
IF IT FAILS

What to do

  • Label the instrument 'Out of calibration' and stop using it.
  • Investigate the cause and arrange adjustment or repair.
  • Assess the impact on results generated since the last passing calibration.
  • Repeat the full calibration before returning it to use.
In LimsPulse · Calibration Management

LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.

See how