Portable field maintenance tool with resistor network for intrinsically safe operation

A method of communicating with a transmitter field device, the method comprising:

• communicatively connecting, via a wired link, a set of terminals of a portable field maintenance tool to a transmitter field device external to the portable field maintenance tool;
• supplying power from the portable field maintenance tool, via the wired link, to the transmitter field device to power the transmitter field device in an intrinsically safe manner such that no voltage on the wired link exceeds 29 volts;
• receiving by the portable field maintenance tool, via the wired link, a communication signal superimposed on the supplied power;
• and
• limiting a voltage drop at the set of terminals, associated with the communication signal and the supplied power, to between a minimum voltage threshold and a maximum voltage threshold by:
• (i) limiting the supplied power so that the voltage drop does not exceed the maximum voltage threshold;
• and
• (ii) activating or deactivating one or more resistors of a resistor network disposed within the portable field maintenance tool and electrically connected to the set of terminals so that the voltage drop remains above the minimum voltage threshold.

A method of communicating with an actuator field device comprising:

• communicatively connecting, via a wired link, a set of terminals of a portable field maintenance tool to an actuator field device external to the portable field maintenance tool;
• supplying power from the portable field maintenance tool, via the wired link, to the actuator field device to power the actuator field device;
• limiting the supplied power in an intrinsically safe manner so that the set of terminals do not exceed a maximum electrical threshold of 29V;
• and
• transmitting by the portable field maintenance tool, via the wired link, to the actuator field device a communication signal superimposed on the supplied power.

A portable field maintenance tool comprising:

• a housing;
• a set of terminals accessible from the exterior of the housing and electrically connectable, via a wired communication link, to a field device that transmits or receives a communication signal via the wired link;
• a communication circuit, disposed within the housing and electrically connected to the set of terminals, that receives or transmits the communication signal via the set of terminals and the wired communication link;
• an energy measurement circuit, disposed within the housing and electrically connected to the set of terminals, that measures one or more electrical characteristics of the communication signal at the set of terminals simultaneously to the communication signal being transmitted or received by the communication circuit;
• and
• a power supply, disposed within the housing and electrically connected to the set of terminals, that is configured to provide power to the field device, via the set of terminals and the same wired communication link used to transmit or receive the communication signal, in an intrinsically safe manner such that no voltage across the set of terminals exceeds 29V, wherein the power supply is configured to provide the power simultaneous to both:
• (i) a transmission or reception of the communication signal via the wired communication link;
• and (ii) a measurement by the energy measurement circuit of the one or more electrical characteristics of the communication signal.

A method of communicating with a field device and monitoring signals sent or received by the field device, the method comprising:

• electrically connecting, via a wired link, a field device to a set of terminals of a portable field maintenance tool;
• transmitting or receiving, at the set of terminals of the portable field maintenance tool and via the wired link, a communication signal to or from the field device;
• measuring, at the set of terminals, one or more electrical characteristics of the transmitted or received communication signal simultaneously to the communication signal being transmitted or received;
• and
• providing power, via the set of terminals and the wired link, from the portable field maintenance tool to the field device to power the field device in an intrinsically safe manner such that no voltage on the wired link exceeds 29V.

A portable field maintenance tool comprising:

• (A) a housing;
• (B) a communication interface that is disposed through the housing, the communication interface including an internal portion accessible within the housing and a set of terminals accessible outside the housing, the set of terminals electrically connectable to a field device by way of a wired link configured to carry a composite signal including:
• (i) a communication signal transmitted to or from the field device, and (ii) a power signal transmitted to the field device;
• (C) a communication circuit disposed within the housing and electrically connected to the internal portion of the communication interface, the communication circuit configured to encode or decode the communication signal;
• and
• (D) a power supply disposed within the housing and electrically connected to the internal portion of the communication interface and to the communication circuit, the power supply configured to transmit the power signal;
• wherein the communication circuit includes a resistor network including a plurality of resistor sub-networks arranged in a parallel configuration, the plurality of resistor sub-networks including first resistor sub-network having a resistance within a range of 200 ohms to 300 ohms, a second resistor sub-network having a resistance within a range of 400 ohms to 600 ohms, and a third resistor sub-network having a resistance within a range of 700 ohms to 800 ohms;
• wherein the resistor network has a total resistance within a range to cause a voltage drop, at the set of terminals, associated with the composite signal, the voltage drop being:
• (i) above a minimum voltage threshold associated with reading the composite signal, and (ii) below a maximum voltage threshold.

A method of communicating with a field device and monitoring signals sent or received by the field device, the method comprising:

• electrically connecting, via a wired link, a field device to a set of terminals of a portable field maintenance tool;
• transmitting or receiving, at the set of terminals of the portable field maintenance tool, a signal to or from the field device;
• measuring, at the set of terminals, one or more electrical characteristics of the transmitted or received signal;
• performing an analysis of the one or more electrical characteristics to determine whether or not the field device is connected to an external loop resistor;
• preventing an internal loop resistor from activating when the analysis reveals that the field device is connected to an external loop resistor;
• and
• activating the internal loop resistor when the analysis reveals that the field device is not connected to an external loop resistor.