HEATER CONTROL SYSTEM

Abstract

A heater control system having an electric heating elements powered from a three-phase alternating current source through a solid state relays connected to the controller and provided with the safety switch assembly is characterized in that each of the heating elements (G) is connected with a separate proportional control solid state relay (K1, K2 K3) and all the proportional control solid state relays (K1, K2, K3) are connected to the controller (S) through the control signal follower (W).

Claims

1. The heater control system having an electric heating elements powered from a three-phase alternating current source through a solid state relays connected to the controller and provided with a safety switch assembly characterized in that each of the heating elements is connected to a separate proportional control solid state relay, and all the proportional control solid state relays are connected to the controller through the control signal follower.

2. The system according to claim 1 characterized in that the control signal follower is an operational amplifier, the input of which is connected to the analog output of the controller of low amperage, and the output is connected to a control input of each of the three heating elements connected in the symmetric delta configuration.

3. The system according to claim 2 characterized in that the control signal follower is supplied from an external source.

Description

[0010] An embodiment of the heater control system according to the invention is illustrated in the drawing, in which FIG. 1 shows a configuration of supply and control, and FIG. 2 shows a configuration of a control signal follower.

[0011] In the exemplary embodiment, the heater control system is designed to the ventilation heater having three heating elements G connected in a symmetric delta configuration supplied from the three-phase power system AC 400 V, 50 Hz. The system is equipped with a main switch Q and a safety switch assembly consisting of the electromagnetic contactor K1 combined with thermostat A and pressure switch B. The thermostat A measures the temperature inside the heaterif it exceeds a certain value, the disconnection of power supply occurs. Using a pressure switch B a static pressure fan measurement is implementedif the fan is not working, the power will not turn on. Each of the three heating elements G is connected to the separate proportional control solid state relay K1, K2, K3. The control input of each of the proportional control solid state relays is connected to the output of the operational amplifier which is a control signal follower W, the input of which is connected to the analog output controller S of a low current efficiency. [0012] A control signal follower is 24 V voltage supplied from an external power source Z, in order not to overload the controller. Controller S according to one of the two common industry standards performs the analog output in the range of 0-10 V, low current efficiency. Each of the used proportional control solid state relays K1, K2, K3 requires a control current of 20 mA maximum value. Simultaneous control of three such relays requires a total control current of 60 mA maximum, which creates an excessive burden for a single controller S. A control signal follower W separates the controller S output of the control current load of the proportional control solid state relays K1, K2, K3 and strengthens the control signal being fed from the controller S. The system uses relays which are controlled by current signal 4-20 mA, and the control signal follower W is realized in the form of the operational amplifier in the system providing the input impedance of over 70 of the output stage on the bipolar transistor with high current-carrying capacity. An analog signal according to the industry standard 0-10 V, max 1 mA is being fed from the controller S to the input of the control signal follower W, and its output signal is 0-10 V, max 100 mA, providing required for the simultaneous control of the three relays value of the control current in the range of 12-60 mA.

[0013] The system according to the invention, by using proportional control solid state relays provides a more effective control of the heater heating elements extending their service life and the use of a control signal follower enables to control this type of relays by a typical industrial controller instead of a separate controller for each relay.