Bath tub

The bath includes a container and a liquid medium. If the required temperature is not significantly different from room temperature, a circular glass cylinder with a capacity of 20dm3 can usually be used as a container. If the set temperature is high (or low), the entire tank should be insulated to reduce heat transfer rate and improve temperature control accuracy.

A constant temperature water bath uses distilled water as the working medium. If the device is slightly modified and other suitable liquids are selected as the working medium, the above-mentioned constant temperature bath can be used over a larger temperature range.

thermometer

A mercury thermometer with a division value of 0.1 ℃ can be used to observe the temperature of the constant temperature bath, while a Beckman thermometer should be used to measure the sensitivity of the constant temperature bath. The installation position of the thermometer should be as close as possible to the measured system. The readings of the mercury thermometer used should be calibrated.

blender

The mixer is driven by a small electric motor with a power of up to 40W, and the mixing speed can be adjusted using a gearbox or transformer. The mixer should generally be installed near the heater to quickly transfer heat and ensure uniform temperature in all parts of the tank.

heater

When setting a temperature higher than room temperature, it is necessary to continuously supply heat to compensate for the heat lost from the water bath to the environment. The selection principle of electric heaters is small heat capacity, good thermal conductivity, and appropriate power. If a bath with a capacity of 20dm3 requires a constant temperature between 20 and 30 ℃, a 200-300W electric heater can be used. When the room temperature is too low, a higher power or two sets of heaters should be used.

Mercury contact thermometer. Mercury contact thermometer, also known as mercury conductivity meter.

The upper part of the mercury ball is welded with a metal wire, and the upper part of the thermometer has another metal wire, which is connected to the signal feedback end of the relay through a lead wire. The top of the contact thermometer has a magnetic spiral adjustment cap, which is used to adjust the height of the metal wire contact. At the same time, the approximate temperature control setting value can be estimated by adjusting the position of the indicator nut on the scale from the thermometer. When the temperature of the bath rises, mercury expands and rises to the contact point. The relay coil is energized to generate a magnetic field, and the circuit breaker jumps off, causing the heater to stop heating. Subsequently, the heat from the bath diffuses outward, causing the temperature to drop. Mercury contracts and disengages from the contacts, causing the electromagnetic effect of the relay to disappear. The spring rebounds, and the heater circuit is connected, causing the system temperature to rise again. This way, the contact thermometer works repeatedly. And the system temperature is controlled. It can be said that it is the center of a constant temperature bath and plays a key role in maintaining a constant temperature.

relay

The relay must be connected to the heater and contact thermometer in order to achieve temperature control. The commonly used relays in the laboratory include tube relays and transistor relays.

The quality of a constant temperature water bath can be measured by its sensitivity. The sensitivity is usually expressed as half the difference between the measured high and low temperature values.