Glossary of Terms

Here you will find a glossary of specialised terms commonly used in thermostating and metrology.

C

Calibration thermostat

A bath thermostat with especially high temperature stability and especially consistent spatial temperature distribution. The test samples used in the bath are compared with a temperature reference standard (calibration) and adjusted to the desired value as necessary.

Cascade control

See external control.

Circulation chiller (also circulating chiller)

A special cooling thermostat which is designed exclusively as a circulation thermostat. Circulation chillers are designed as independent units in terms of their type of construction, the cooling and pump capacities. They are often used as a substitute for mains water-cooling.

Circulation thermostat

A thermostat in which the bath liquid is conveyed through an open or closed external circuit. Circulation thermostats can have a thermally decoupled active surface, as in the case of the USH 400 and the process thermostats, whose surface temperature does not match the operating temperature. They do not have a freely accessible bath.

Clear-view thermostat

A bath thermostat with a transparent back and front for direct observation of the tempering object preferably viscometers. Bath thermostats with transparent plastic baths are described as thermostats with a transparent bath and not as clear-view thermostats in the narrower sense.

CMC measuring

The determination of the surfactant concentration at which the surfactant molecules begin aggregating into micelles (CMC concentration). This can be determined from the dependency between the concentration of the surfactant in the solution and the surface tension.

Compressor control

See injection control.

Component tested safety facilities

As a rule all temperature control units fall within the pressure equipment directive (see DGRL 97/23 EC). Depending on the heat transfer medium and the temperature, the installations have to be equipped with special safety facilities, for example safety valves, pressure, temperature or leveling switches. These facilities serve as a protection for the temperature control unit at exceeding the admissible limits of the application. In this connection it has to be strictly observed that only component-tested parts, i.e. qualified components, from a named testing laboratory are used. These components have to be equipped with the identification numbers of the named testing laboratory and conformity declarations of the manufacturers have to be on hand.

Condenser

See refrigerant.

Contact angle/contact angle measuring

characterizes the wetting properties of liquids on solid bodies. The contact angle can be determined by measuring individual drops on a solid or from the forces required to move a solid in contact with a liquid lamella. The contact angle is used to calculate surface energy.

Control circuit

Control circuit is the totality of control section (see control section) and controller. Sensors and signals, their processing and transmission also form part of the control circuit. For example, transformers, clamps and electric lines.

Control deviation

Control deviation is the deviation of the actual value from the preset setpoint.

Control section

Control section is the part of the control circuit to be influenced according to its application. Pipework, sensors and heat transfer areas with their walls and coatings also form part of the control section. Through distances from the test point to the final control element and through inertia at the heat transfer for example, a characteristic response time of a control section arises. Depending on the response time, a control section is classified from 'good' to 'difficult'.

Control variable

Adjusting command of the controller that acts on the so-called actuator.

Controller characteristic

Different controllers are distinguished according to their so-called controller characteristic: proportional response (P-controller), integral response (I-controller) and differential response (D-controller). As for temperature controllers, combined characteristics have stood the test. Modern PID-controllers can be perfectly adapted to difficult control sections through freely eligible parameters. They are therefore widely used.

Controlling temperature

To control temperature means to control supply or carry away heating or cooling energy in order to reach a constant temperature at the consumer.

Cooling capacity

The effective capacity available in cooling thermostats or circulation chillers. The friction heat produced by the circulating pump and the heat penetrating as a result of insulation that is not ideal has already been taken into consideration.

Cooling capacity adjustment, automatic

Provided with the more powerful Ecoline cooling thermostats, this is a procedure to save energy. The controller determines by a suitable logic in the microprocessor whether it is possible according to the operating temperature and the cooling demand to set the required cooling capacity to a lower level. In addition to saving energy, this also saves wear and tear of the compressor, reduces the amount of heat given out to the environment, and gives better temperature stability.

Cooling cascades

If temperatures below -50 °C are to be produced with compression cooling units, so-called two-stage cooling units connected in cascades are required to bridge the difference between the cold side (evaporation pressure) and warm side (condensation pressure, e.g., ambient temperature). The high-pressure stage bridges the temperature difference from approximately ambient temperature down to -40 °C, for example. The low-temperature stage condenses at -35°C and evaporates at -90°C, for example. This requires special refrigerants with the corresponding thermodynamic characteristics.

Cooling power

With medium cooled heat exchangers the cooling capacity always depends on the temperature difference between cooling medium and heat transfer fluid. The cooling capacity reduces at falling outflow temperature and tends to zero when it reaches the cooling medium temperature. At mechanical cooling the characteristics are similar. The cooling capacity thus always relates to a definite outflow temperature. At LAUDA the performance data of refrigeration machines is based on cooling water or air with a temperature of 20°C.

Cooling thermostat

A thermostat whose working temperature range is also below the ambient temperature and preferably draws heat from the thermostating liquid.

Correction as per Harking and Jordan

Harkin and Jordan produced tables for correcting surface and interfacial tensions measured with a ring. These values are standardized.

Cracking

Breakdown of a liquid is produced by contact with oxygen at high temperatures or through high film temperatures on the heater. Cracking can be reduced by keeping the bath opening to a minimum. In addition the heaters of LAUDA thermostats are of optimal design so that unnecessary high film temperatures are avoided.

Critical micellar concentration (CMC)

At this concentration, surfactant solutions suddenly change their physical properties. The reason for this is the formation of organized aggregates (micelles) of the surfactant molecules when the critical micellar concentration is exceeded. The structure of the micelles is dependent on the character of the solvent and the structure of the surfactant molecules.

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