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What is TUS? How to do it?

Updated: Jun 24

Temperature uniformity survey (TUS) is a test performed to measure homogeneity in heat treatment furnaces.


TUS fram per AMS 2750G

To fully understand this test, we need to take a look at a term defined in AMS 2750G.


2.2.76 TEMPERATURE UNIFORMITY: The temperature variation (usually expressed as ± degrees) within the qualified work zone with respect to set point temperature. For retort furnaces where a sensor in the retort is used to control temperature, the temperature variation is with respect to the sensor in the retort and not to the furnace set point temperature. The requirement is established by the required thermal processing equipment class in accordance with Table 8.


In other words, temperature homogeneity can be defined as ±5°C temperature readings in different regions in an oven set to 1040°C. This describes a Class 2 furnace according to AMS 2750G Table 11.


After this explanation, let's look at the definition of TUS in AMS 2750G,


2.2.79 TEMPERATURE UNIFORMITY SURVEY (TUS): An assessment of the temperature variation within the qualified work zone of thermal processing equipment prior to and

after stabilization using a field test instrument (TUS recorder) meeting Table 7 requirements and sensors meeting the requirements of Tables 1, 17, and 18, as applicable.


Let's take a look at how TUS is defined in CQI-9:


Temperature Uniformity Survey (TUS): A test or series of tests in which a calibrated field test device and calibrated test thermocouples are used to determine the temperature variation within a qualified operating zone. This testing process aims to verify the temperature distribution, qualified operating zones, and qualified operating temperature ranges of furnace and furnace systems.


How is TUS done?

It is done by using sensors (thermocouples) placed at the furthest points of the furnace and the furnace heating parameters used in production. Of course, both the sensors and the recorder must meet the requirements of the relevant standard (AMS 2750G, CQI-9 or ASTM A991).


What are the outputs of TUS?

  • The hottest and coldest point in the oven at a given temperature

  • Behavior of the oven when approaching the set temperature (overshoot or failure to reach that temperature)

  • Relationships of sensors with each other (recovery time)

  • After the oven reaches the set temperature, the temperature tends to rise or fall at the extreme points of the oven.

  • If it is done in a loaded way, the effect of issues such as the number and placement of parts to be heat treated in that furnace on the homogeneity of the furnace.

Temperature distribution research
A TUS chart made with 9 different sensors at three different temperatures

How can BDI Metal help you?

With the experience gained from being in this industry for many years, we can provide you with TUS service according to the required standard in different furnace types or to see the general condition of the furnace.




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