This is a guide to temperature gauge selection including the thermometer sensor and thermowell. By following what explained here you will discover how to define the best part used in temperature gauge that suits your need to.
Temperature gauge’s stem is available in some offers pertinent to the connection to the thermowell or the process. There are threaded, plain and union.
Thermo gauge with union stem uses union method to connect the gauge to the thermowell or the process.
2. Stem Connection Size
This usually within ½ inch but you can conform to the design
3. Stem Diameter
Stem diameter is a diameter of sensor which there is a bimetal sensor within. In standard it uses manufacturer’s design but you can specify to your design. E.g. 0.250 inch or 0.375 inch
4. Case Material
Case material need to be specified as what you need to. If you need to prevent from corrosion then you can choose stainless steel. Case material is available in Aluminum, 316 SS, Black Phenolic and other. You can ask to the manufacturer.
5. Dial Size
Dial size can be any size. The point is it can give the clear vision while conduct inspection. For example if the gauge is placed 3 meters under the ground and the inspector see it from the ground then I am sure it needs large dial size as 4.5” or more.
6. Scale Length
The best practice is using a gauge that manufactured at least 200% of normal process operation. For example, if the normal operation runs in 70 degree then the gauge should be 140 degree or greater.
In this stage there are two option i.e. fixed and adjustable
8. External Calibration
The condition of a gauge will not same as new after it operates for long period. This is caused by the material condition after get treatments like static process condition, climate change and other. However, the gauge still has its function, you just need to check and calibrate it periodically. So that you need the calibration set internal or external.
Internal calibration: the set is inside of the case (covered, you need to open the case to calibrate)
External calibration: the set can be accessed without open the case
9. Glass/ Window
The dial need to be covered. There are glass, plastic ………………
You need to specify the accuracy you need. Standard it goes for 0.5% of the full scale.
It needs to fit to your connection. The connection is defined to fit the installation. It can be back or bottom
12. MFR. & Model No.
If you already find what vendor you need then you can write down here.
Type of temperature sensor. It can be bimetal or liquid/gas expansion
You can specify whether you need vendor to include the thermowell or not, you can buy the thermowell from other vendor though.
This is material of thermowell not the thermometer.
16. Bore size
Bore size of the thermowell
How the thermowell was made
18. P&ID No.
The no of the device in P&ID
19. Manufacturer name
If you already specify the vendor to supply then write down here the brand