Sanitary Platinum Thermistor

Sanitary Platinum Thermistor

★ Principle and Structure

The structure and principle of explosion-proof thermistor and assembled thermistor are basically the same. The difference is that the junction box (shell) of explosion-proof products adopts a special explosion-proof structure in the design. The junction box is made of high-strength aluminum alloy die-casting and has sufficient internal space, wall thickness and mechanical strength. The thermal stability of the rubber sealing ring meets the national explosion-proof standard. Therefore, when the explosive mixed gas inside the junction box explodes, its internal pressure will not damage the junction box, and the resulting heat energy cannot be discharged outward

Sanitary Platinum Thermistor

★ feature

1）Structural features: Due to high hygiene requirements, the surface of the product should minimize dead corners and structures that are difficult to clean, and comply with the installation methods of food or drug processing equipment systems, such as using DN25, DN50 clamps, spherical welding pads, or fully enclosed waterproof and anti-corrosion structures. In some special occasions, the protection level should reach IP68.

2) Material requirements: For general sanitary temperature sensors, use all stainless steel or stainless steel materials for parts that come into contact with liquids, products, and measuring media. The material should be 316 or 316L grade or above. At least 304 or higher grade stainless steel is used for junction boxes and accessory materials (referring to accessories for non-contact products), and a small number of low-end products also use aluminum alloy accessories. In some special occasions and sealing materials, medical grade or food grade non-metallic materials such as medical silicone, medical PTFE, and food lubricants can also be used. These structures are easy to clean (acid wash) by CIP and can achieve the relevant corrosion level.

3) Surface treatment: Due to different application scenarios, it is generally required that the product surface is easy to clean and has a certain degree of smoothness, especially for the parts in contact with the product, to achieve a surface roughness Ra<0.4 μ m, with or without electrolytic polishing.

4) Temperature sensing element: Before the widespread use of platinum resistors, sanitary temperature sensors generally used K-type and T-type thermocouples (there are still a few low-end and special occasion thermocouples). After the widespread use of platinum resistors, most sanitary temperature sensors now use platinum resistors, such as PT100 and PT1000. However, in some special occasions, such as inspecting cooked meat processing products, piercing thermocouples and curved armored thermocouples are still used in the food and pharmaceutical industry. Most sanitary temperature sensors use PT100, with an accuracy level of * or A *. In high demand scenarios, redundant dual platinum resistors are used.

5) Electrical output methods include direct resistance signals, 4-20mA after transmission, or Hart communication methods

★ Model and specifications

Industrial thermal resistors are divided into two categories: platinum thermal resistors and copper thermal resistors.

Thermistor measures temperature by utilizing the characteristic that a substance's own resistance changes with temperature. The heated part (temperature sensing element) of a thermal resistor is uniformly wound around a skeleton made of insulating material with thin metal wires. When there is a temperature gradient in the measured medium, the measured temperature is the average temperature in the dielectric layer within the range of the temperature sensing element.

Prefabricated thermistor mainly consists of a junction box, protective tube, terminal block, insulation sleeve, and temperature sensing element, and is equipped with various installation and fixing devices.

The temperature sensing element of WZP type platinum resistor is a platinum wire winding, and dual platinum resistors are mainly used in situations where two sets of display, recording, and regulating instruments are required to simultaneously detect the temperature at the same location. The temperature sensing element of WZC type copper resistor is a copper wire winding

The ratio of the resistance value (R100) of a thermistor temperature sensing element at 100 ℃ to its resistance value R0 at 0 ℃: (R100/R0)

Division number Pt100: Class A R0=100 ± 0.06 Ω

B-class R0=100 ± 0.12 Ω

R100/ R0=1.3850

Index number Cu50: R0=50 ± 0.05 Ω

★ Model representation