What Is a Dial Thermometer?
A dial thermometer is a temperature measurement device featuring a circular display and a rod-shaped sensing element. It may use a bimetal or Bourdon tube mechanism to mechanically move the indicator. Known for their robustness and ease of maintenance, dial thermometers are extensively used in industrial settings. Many models include three-pointers for temperature indication, maximum temperature indication, and alarm signaling.
Uses of Dial Thermometer
Dial thermometers are primarily used for measuring transformer temperatures, monitoring oil temperature near coils, and bearing temperature in rotating machinery. In electrical substations and facilities, they play a critical role in detecting temperature rises during operations or overload conditions. While they lack built-in alarm functions, many are equipped with alarm contact points that trigger external devices like lamps or buzzers for warnings. Their applications span various industries, including refrigeration, food production, biotechnology, pharmaceuticals, machinery manufacturing, heating devices, cooling systems, ventilation, solar collectors, hot water tanks, and heat transfer stations.
Principle of Dial Thermometer
1. Bimetallic Thermometer
Bimetallic thermometers use two metal plates with different thermal expansion coefficients. The differential expansion causes bending, which moves a pointer on the display to indicate temperature changes.
2. Gas/Liquid Expansion Thermometer (Pressure-type Thermometer)
These thermometers operate on the principle of gas or liquid volume changes with temperature variations. The sensing bulb, conduit, and Bourdon tube form a sealed system filled with fluid. Temperature changes cause fluid expansion or contraction, affecting the pressure in the Bourdon tube, which is then reflected on the dial.
Types of Dial Thermometers
1. Classification by Function
Dial thermometers vary by function, including models with maximum temperature indicators and hybrid types that offer direct and remote readings. Shock-resistant models are also available, using glycerin to absorb vibrations.
2. Classification by Exterior
In hygiene-sensitive environments like food processing or pharmaceutical plants, dial thermometers are designed with features like electrolytic polishing or stainless steel construction. They come in various forms, including wall-mounted and panel-mounted designs. For challenging environments such as electroplating or chemical plants, there are models with enhanced chemical resistance.