Hygienic temperature sensors, also known as temperature sensors for the food and pharmaceutical industries, are generally used in the food processing and pharmaceutical processing industries, and are also expanding their application to the biochemical products and fine chemical industries. They comply with FDA GMP standards.
1) Structural features: Due to the high hygiene requirements, the product surface should have as few dead corners as possible and structures that are not easy to clean. It should also conform to the installation methods of food or pharmaceutical processing equipment systems, such as using DN25, DN50 clamps and spherical welding pads, or a fully enclosed waterproof and corrosion-resistant structure. In some special cases, it can reach the IP68 protection level.
2) Material Requirements: Generally, hygienic temperature sensors use all stainless steel, or stainless steel in parts that come into contact with liquids, the product, and the measured medium. The material should be 316 or 316L grade or higher. Junction boxes and accessories (referring to non-contact product accessories) should also use at least 304 grade stainless steel; a small number of lower-end products may use aluminum alloy accessories. In some special applications and for sealing materials, medical-grade or food-grade non-metallic materials may be used, such as medical-grade silicone, medical-grade PTFE, and food-grade lubricants. These structures facilitate CIP cleaning (acid pickling) and meet the relevant corrosion resistance standards.
3) Surface treatment: Due to different applications, the product surface is generally required to be easy to clean and have a certain degree of smoothness, especially the parts in contact with the product, which should achieve a surface roughness Ra<0.4μm, and may or may not be electrolytic polishing.
4) Temperature sensing element: Before the widespread use of platinum resistance thermometers, sanitary temperature sensors generally used type K and type T thermocouples (a small number of low-end and special applications still use thermocouples).
With the widespread use of platinum resistance thermometers (PTTs), most sanitary temperature sensors now use PTTs, such as PT100 and PT1000. However, in some special applications, such as inspecting processed cooked meat products, insert thermocouples are used, and flexible armored thermocouples are still used in the food and pharmaceutical industries. Most sanitary temperature sensors use PT100, with an accuracy class typically A or AA. For applications requiring higher accuracy, redundant dual-plasma resistance thermometers are used.
5) Electrical output methods include direct resistance signal or 4-20mA, 0-5V, 0-10V after transmission, or HART communication and RS485 Modbus.
Technical parameters:
Platinum resistance thermometers: Pt100, Pt500, Pt1000 (-200～600)℃
IEC 60751 specifies the accuracy classes:
Grade C: 0.5 ± (0.50K + 0.006xItI);
Grade B: 0.3 ± (0.30K + 0.005xItI);
A: 0.15 ± (0.15K + 0.002xItI);
2A: 0.1 ±(0.10K+0.0017xItI); Note: ItI is the absolute temperature value.
Below are some commonly used types of sanitary temperature sensors.
