Environment Friendly Science Instruments

Weiber is committed to provide totally environmental friendly cooling solutions working closely with our clients to pinpoint the problems inherent in maintaining the consistent temperatures for analytical and research applications.

The effective capacity a cooling unit can provide for application at designated room temperature and test conditions. Unit for cooling capacity is watts or Kcal/hr. Cooling capacity is one of the most important specifications one must confirm when choosing a cooling unit, It has something to do with the deepest temperature a cooling unit may reach. This doesn’t mean that a cooling unit with lower temperature has more cooling capacity. For example, an application will produce 380W heat at-20 °C test condition. There are 2 units to choose from. The temperature range for one unit is -30~+90 °C, with cooling capacity 480W@-20 °C. The temperature range for another unit is -50~+90 °C, with cooling capacity 350W@-20 °C. When only cooling capacity or even price is considered, the first unit better choice.

Varieties of controllers with different temperature stability, dynamic capability, display resolutions and auxiliary functions are designed and configured to be assembled to thermostatic equipments for different applications. The temperature stability and dynamic capability are dependent on the algorithm of the temperature controller. On.off control is the most simple, economic and reliable way for temperature regulation. The load is fully cut in and cut out from the circuit with settable temperature difference from setting. The on/off control applicable to applications where temperature stability is less important or static stable system where temperature regulation is minimum. The best stability is expected to be +0.1~0.5 °C. Improved proportion control (or PWM) regulates the load to be cut in and off the circuit at finer intervals only when temperature approaches the set point, thus keeping it precisely around the setting. Stability of around +0.02~0.1 °C is expectable. Advanced PID control is able to predict the temperature change and regulate the load in advance. One doesn’t have to compromise between stability and speed, which makes it applicable to ever-changing load system or applications where precise temperature regulation is desired.

The temperature stability is expected to be in the range of + 0.002~0.5 °C. The display resolution is designed to match the stability of the controllers and their applications. For the above- mentioned controllers, the resolution are 0.1 °C, 0.1/0.01 °C and 0.01/0.001 °C respectively, with the latter to programmable by the user. The auxiliary functions may differ from units to units. As standard for controller designed, absolute temperature calibration (ATC), safety function and auto-restart after power failure are incorporated in all controllers. Temperature, humidity and light editing and programming, auto-start, auto-stop and timer, and Rs 232/485 communication interface are included in part of Weiber’s controllers.

Precision is the repeatability of successive measurements at the same test condition and the accuracy is the difference between the measured reading and the true value traceable to national standard. The temperature stability describe under the specifications refer to precision, and has nothing to do with the difference from the true temperature. When accurate reading is expected, periodic absolute temperature calibration (ADC) procedure is necessary by using a standard thermometer according to the metrological regulations. Generally controller with 0.001o C resolutions can be calibrated to 0.5 O C accuracy, while 0.01O C and 0.0010 C resolutions to 0.1O C and 0.05O C accuracy. All controllers provided by Weiber are 100% calibarated according to Weiber’s standard before being assembled into products, and are featured with ATC capability.

The range of maximum temperature and minimum temperature a temperature regulated equipment (baths, circulators or chambers) is able to maintain or control. The minimum temperature of the equipment with no cooling unit incorporated depends on room temperature, and normally is 5….10 °C higher than the ambient. This comes from the heat emission from fan/pump motor and impeller friction. As a reference, the minimum temperature for a heating bath is 25 °C when operating at 15 °C room temperature, is 38 °C at 28°C room temperature. Lower the minimum temperature is possible by a heat exchanger (cooling coil or fin-tube condenser) incorporation when cooling source is already available, including deep-well water, dry ice and liquid nitrogen and provided that the insulation and the controller meet the requirement of the temperature extension. For equipments with cooling unit already incorporated, unit the minimum temperature is not only dependent on the room temperature, the heat demand of the application should not exceed the cooling capacity at the designated temperature. Otherwise, you will find it difficult to keep the temperature. The maximum temperature is largely influenced by the maximum temperature of the controller, insulation material at the working area, sealing material at the door and I the cover, circulating pump and fan, and liquid medium for the bath, and can not be extended at will. Not all the refrigerating system are designed to work continuously at the entire temperature range. For example the temperature range of a bath is -60~+95°C. One application could be to test the physical property of a chemical at -40 °C, -20 °C, 0 °C, +10 °C, +30 °C, and +60 °C temperatures.

These tests require that the temperature range, temperature stability and the cooling capacity at corresponding temperature be in the range. Another application is to test the sample property under continuously changing temperature range sinuously programmed as follows: centre temperature 0.0 °C, amplitude 40.0 °C, original phase angle 0.0, time period 12hr. With this application, the temperature change at zero- crossing point (0 °C) is very fast, while at top (-40 °C) and valley (+40 °C) of the curve, the temperature change is very slow. Because of the basic requirement of smooth and continuous temperature programming, cooling capacity switching during the process is not permitted. This requires that the controller feature excellent static and dynamic temperature control capability, the refrigerating system needs to be strictly designed to match the application. Although the temperature range is the same, the software editing of the controller and configuration of the cooling unit is completely different with application.