US 5,970,226 A · Method of non-intrusive testing for a process control interface system having triply redundant remote field units

Abstract

A process control interface system having a network of distributed triply redundant input/output field computer units. The system includes a plurality of self-contained remotely located triply redundant field computer units connected to decision making redundant process control computers through a bi-directional communication network having at least two concurrently active communication channels. Each of the field computer units include a set of at least redundant field computers for arbitrating both input and output signals. The input arbitration method enables a plurality of selectable default input conditions, such as select HIGH and select LOW, in the event that a majority agreement cannot be reached among valid input signals. The output arbitration method includes a plurality of selectable default output conditions, such as fail SAFE and fail LAST. Each of the default input and output conditions may be rapidly adjusted through software selection. The field computer units also include individual abort circuits for each output signal to be transmitted to a device which affects the operation of the physical process. These abort circuits effectively enforce the output value signals arbitrated independently through each of the three redundant field computers using a voting procedure.

Claims27

Dependent claims

A method of conducting passive non-intrusive testing of a set of corresponding digital output circuits in a field computer unit having at least three redundant computers, where each of said digital output circuits having a plurality of output channels, comprising the steps of:

providing a predetermined period of time in which to conduct a passive test of a plurality of said output channels;
and
conducting passive testing of a plurality of said output channels during said predetermined period of time,
said passive testing for each of said plurality of output channels including the steps of comparing the magnitude of a first signal with a first predetermined high test level when said channel is On, and comparing the magnitude of a second signal with a predetermined low track signal when said channel is Off,
said first and second signals being different signals associated with said digital output circuit and each of said comparing steps providing a determination of a different error condition.

2 more elements

A method of non-intrusively testing a digital output circuit in a field computer unit having at least three redundant digital output circuits which are each controlled by a correspondingly redundant computer, where each of said digital output circuits has a plurality of output channels and each of said output channels has a power switch controlled by one of said redundant computers and a set of abort switches which are each controlled by a neighboring redundant computer, comprising the steps of:

(a) selecting a first output channel to be actively tested on one of said digital output circuits;
(b) determining whether the selected output channel is in an On condition where said power switch is closed and at least one of said abort switches is closed, or an Off condition where at least said power switch is open;
(c) conducting a series of active-Off tests if the selected output channel is in an Off condition;
(d) conducting a series of active-On tests if the selected output channel is in an On condition;
(e) selecting the next output channel to be actively tested on one of said digital output circuits, and repeating steps (b) through (d) for the next output channel to be actively tested;
and
(f) periodically repeating steps (b) through (e) until all of said output channels for all of said digital output circuits are actively tested.

4 more elements

providing a predetermined period of time in which to conduct a passive test of a plurality of said output channels;
conducting passive testing of a plurality of said output channels during said predetermined period of time regardless of whether said output channels are On or Off,
selecting at least one of said output channels for one of said digital output circuits for active testing after said predetermined period of time has expired;
and
conducting a series of active tests, said active tests including a plurality of active-Off tests if the selected output channel is in an Off condition and a plurality of active-On tests if the selected output channel is in an On condition.

2 more elements

A method of non-intrusively testing an analog output circuit in a field computer unit having at least three redundant analog output circuits which are each controlled by a correspondingly redundant computer, where each of said analog output circuits has a plurality of output channels and each of said output channels has an analog signal driver which is responsive to one of said redundant computers and a set of abort switches which are each controlled by a neighboring redundant computer, comprising the steps of:

(a) selecting one of said analog output circuits to undergo said non-intrusive testing;
(b) causing an analog signal driver for at least one of said output channels of said selected analog output circuit to reduce its analog signal level to a predetermined level over a period of time which will permit at least one of said neighboring redundant computers to increase its analog signal level output in order to maintain the analog signal level provided to a field device for this output channel before said non-intrusive testing was begun;
(c) determining if the analog signal level provided to said field device was reduce by a predetermined amount during the time that that analog signal level from said analog signal driver was being reduced;
and
(d) restoring the analog signal level output of said analog signal driver to the analog signal level provided before it was reduced.

2 more elements

Dependencies are inferred from the claim text.

Method of non-intrusive testing for a process control interface system having triply redundant remote field units

Life of this patent

Method of non-intrusive testing for a process control interface system having triply redundant remote field units

Life of this patent

Abstract

Claims27