Low voltage industrial control system providing intrinsically safe operation

A method of operating an industrial controller in a hazardous environment, the industrial controller reading inputs from an industrial process and providing outputs to the industrial process under the direction of a stored control program generating new outputs, the industrial controller having a serial link communicating outside the hazardous environment, the method comprising the steps of:

• (a) placing the industrial controller inside the hazardous area;
• (b) limiting the power supplied to the industrial controller to produce first power signals having a first power level unlikely to produce electrical sparks that will ignite a flammable atmosphere during a fault condition of the industrial controller;
• and
• (c) limiting the power of the first power signals transmitted over the serial link to produce second power signals having a second power level, wherein the second power level is less than the first power level and is unlikely to produce electrical sparks that will ignite a flammable atmosphere during a fault condition of the serial link;
• (d) selectively removing low frequencies from the signals transmitted over the serial link using a high pass filter;
• and
• (e) executing the control program on the industrial controller and communicating inputs and outputs between the industrial controller and the controlled process and as signals on the serial link.

An industrial controller for use in hazardous environments and configured to read inputs from an industrial process and provide outputs to the industrial process under the direction of a stored control program, the industrial controller comprising:

• a power supply limited in output to produce power signals having a sufficiently low power level to avoid the generation of sparks with sufficient energy to ignite a flammable atmosphere during a fault condition in the power supply;
• a serial network port receiving and transmitting data over serial network media using signals limited in power to avoid the generation of sparks with sufficient energy to ignite a flammable atmosphere during a fault condition of the serial network;
• a processor executing the stored program to control an industrial process and to communicate with the serial network and receiving power from the power supply;
• a plurality of interface circuits receiving power from the power signals and communicating electrical signals over interface lines between the industrial controller and the industrial process;
• a high pass filter configured to selectively remove low frequencies from the signals communicated over the interface lines;
• and
• a digital circuitry receiving power from the power supply and communicating data between the serial network port and one of the interface circuits;
• whereby the industrial controller may be operated from a location wholly within a hazardous location.

A method of operating an industrial controller in a hazardous environment, the industrial controller reading inputs from an industrial process and providing outputs to the industrial process under the direction of a stored control program generating new outputs, the industrial controller having a serial link communicating outside the hazardous environment, the method comprising the steps of:

• (a) placing the industrial controller inside the hazardous area;
• (b) limiting the power supplied to the industrial controller to a level unlikely to produce electrical sparks that will ignite a flammable atmosphere during a fault condition of the control unit;
• and
• (c) limiting the power of signals transmitted over the serial link to a level unlikely to produce electrical sparks that will ignite a flammable atmosphere during a fault condition of the serial link;
• (e) executing the control program on the control unit and communicating inputs and outputs between the industrial controller and the controlled process and as signals on the serial link.