- Variable area flow meter, range 100-1000 l/h
- Pneumatic control valve
- Plate heat exchanger E1
- Pressure gauge 0 - 2.5 bar
- Electrical supply light
- Microprocessor controller, PID type
- 2measurement terminals for the 4-20 mA output signal of the controller
- RTD Pt100 with AISI 316 stainless steel sheath, code TT
Description of apparatus:
The unit Mod. TCB/EV enables to study the automatic temperature control using a plate heat exchanger, a control valve (for the flow-rate of the cooling water), an RTD Pt100 and a PID controller. The hot (water) current consists of water produced by a thermostatic bath; the cold current is the main water. The system is provided with a specific supervision software, mod. SW – TCB/EV, that enables its use from the P.C. The bench can be connected in parallel to the other automatic control units (Mod. LCB/EV and FCB/EV).
Experiments done on it:This unit used to control the Temperature of water.
In this unit, the PID control is made on the output temperature of the hot current coming from the plate heat exchanger E1. The control device consists in a pneumatic valve that, according to the signal coming from the PID controller, adjusts the cold current flow-rate. The temperature measurement is carried out by means of an RTD which operating principle can be summed up as follows.
The electrical resistor of a conductor generally increases with the temperature, so from the resistor measurement, obtained with a bridge circuit, you can find out the temperature of the ambient with which a resistor is in thermal balance. The instruments of this kind have the double advantage to be very accurate and very simple and are used in industrial devices with direct reading as well as in temperature measurements with the maximum accuracy (in these cases a wire of pure platinum is used as resistor, in the temperature range between —258 °C and 900 ºC).
The RDT is composed of a very thin metal wire, wound around a small porcelain cylinder and included into an insulating sheath. The wire, that represents the thermometric substance, is connected to a proper electrical circuit created to provide a measurement of the resistance with the maximum accuracy. The RTDs are indicated according to the atomic element that constitutes the wire and according to the zero degree resistance; e.g., the most used ones are the Pt100: platinum RTDs from 100Ω to 0°C. 4 wires normally exit from the RDT: two primaries for the current and two secondaries for the voltmeter.