US 5,444,644 AGranted

Auto-configured instrumentation interface

AssigneeJohnson Service Company

InventorAugust A. Divjak

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Abstract

An instrumentation interface circuit controlled by a microprocessor of a data acquisition system enables identification of the type of input/output devices that are connected to its inputs through a systematic analysis of the characteristics of the connected devices, the systematic analysis including monitoring the current through and the voltage across the devices as different drive signals are applied to the connected devices, the interface circuit including a conditioning circuit having a drive circuit which is controlled by the microprocessor for providing the drive signals, a current sensing circuit for sensing the load current flowing through the connected device, a voltage sensing circuit for sensing the voltage across the connected device, and a switchable feedback circuit which is controlled by the microprocessor to selectively feed back the load current or the sensed voltage to the input of the drive circuit to establish the drive signals for the connected device.

Claims21

Dependent claims

In a data acquisition system including a plurality of input devices and a plurality of output devices, signal processing means operable in a data acquisition mode for monitoring the input devices and controlling the output devices, and a plurality of interface circuits interposed between said input and output devices and said signal processing means for interfacing said devices with said signal processing means, each of said interface circuits comprising:

conditioning circuit means having an input circuit with at least one of said devices being connected to said input circuit,
said conditioning circuit means including drive circuit means coupled to said input circuit for providing a drive signal for said connected device, current monitoring means coupled to said input circuit for providing a signal indicative of the current flowing through said connected device, and voltage monitoring means for providing a signal indicative of the voltage across said connected device,
said signal processing means being programmed to be operable in a configuring mode to control said drive circuit means to vary the drive signal to thereby vary at least one of the current flowing through said connected device and the voltage across said connected device, and said signal processing means processing the signals provided by said current monitoring means and said voltage monitoring means as the current through and the voltage across said connected device and are varied to determine whether said connected device is an input or an output type device and to configure said conditioning circuit means as a function of the type of device connected thereto, said signal processing means identifying said connected device as an input type device when, in the absence of a drive signal, said voltage monitoring means provides a signal and as an output type device when said voltage monitoring means fails to provide a signal, and said signal processing means configuring said conditioning circuit means to enable a connected device that is identified as an input type device to be monitored while said signal processing means is operating in said data acquisition mode, and to enable a connected device that is identified as an output type to be controlled by drive signals provided by said drive circuit means while said signal processing means is operating in said data acquisition mode.

An interface circuit for coupling a plurality of input and output devices to a signal processing means, said interface circuit comprising:

conditioning circuit means having an input circuit adapted for connecting at least one of said devices to said interface circuit;
said conditioning circuit means including drive circuit means having an output coupled to said input circuit for providing a drive signal for said one device, current monitoring means coupled to said input circuit for providing a signal indicative of the current flowing through said one device, and voltage monitoring means for providing a signal indicative of the voltage across said one device;
said drive circuit means including a differential amplifier having feedback circuit means including switching means, said switching means being controlled by said signal processing means in a first mode to feed back to said first input of said differential amplifier a current that is proportional to the current flowing through said one device and operable in a second mode to feed back to said first input of said differential amplifier means a voltage that is proportional to the across said one device, to permit said conditioning circuit to be configured as a function of whether said one device is an input type device or an output type device, enabling the drive signal produced by said drive circuit means to be selected as a function of whether said one device is an input type device or an output type device.

In a data acquisition system including a plurality of input devices, a plurality of output devices, signal processing means operable in a data acquisition mode for monitoring the input devices and controlling the output devices, and interface circuit means interposed between the input and output devices and the signal processing means for interfacing the input and output devices with the signal processing means, a method of determining the types of device connected to the input of the interface circuit means comprising the steps of:

causing said signal processing means to control a drive circuit means of said interface circuit means to vary the current flowing through said connected device and the voltage across said connected device in a predetermined sequence;
monitoring at least one of the current flowing through the connected device and the voltage across said connected device while the current flowing through said connected device and the voltage across said connected device are being varied;
using the current and voltage values measured to determined whether said connected device is an input or output type device, including identifying said connected device as an input type device when, in the absence of a drive signal, said voltage monitoring means provides a signal and as an output type device when said voltage monitoring means provides a signal,
and causing said signal processing means to configure said conditioning circuit as a function of the type of device connected thereto, including causing said signal processing means to configure said conditioning circuit means to enable a connected device that is identified as an input type device to be monitored while said signal processing means is operating in said data acquisition mode, and to enable a connected device that is identified as an output type device said drive circuit means to be controlled by drive signals provided by said drive circuit means while said signal processing means is operating in said data acquisition mode.

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Dependencies are inferred from the claim text.