TWO-WIRE PROCESS CONTROL LOOP CURRENT DIAGNOSTICS
First Claim
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1. A process variable transmitter, comprising:
- a processor receiving an input signal indicative of a sensed process variable and outputting a digital signal indicative of the input signal;
a digital-to-analog (D/A) converter receiving the digital signal and converting it to an analog signal;
a loop control component receiving the analog signal and controlling a two-wire process control loop to provide a transmitter output signal indicative of the analog signal, the transmitter output signal varying, on-scale, between a first signal level and a second signal level; and
a loop diagnostic component, comparing a first signal value indicative of the analog signal with a second signal value indicative of the transmitter output signal to determine whether the transmitter output signal includes an on-scale error and responsively outputting an error indicator to the processor.
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Abstract
A process variable transmitter controls a signal on a communication loop. A diagnostic component on the transmitter compares an expected signal level on the communication loop with an actual value to detect on-scale errors.
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Citations
20 Claims
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1. A process variable transmitter, comprising:
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a processor receiving an input signal indicative of a sensed process variable and outputting a digital signal indicative of the input signal; a digital-to-analog (D/A) converter receiving the digital signal and converting it to an analog signal; a loop control component receiving the analog signal and controlling a two-wire process control loop to provide a transmitter output signal indicative of the analog signal, the transmitter output signal varying, on-scale, between a first signal level and a second signal level; and a loop diagnostic component, comparing a first signal value indicative of the analog signal with a second signal value indicative of the transmitter output signal to determine whether the transmitter output signal includes an on-scale error and responsively outputting an error indicator to the processor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of identifying errors output by a process variable transmitter, comprising:
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controlling a two-wire process control loop to carry an analog output signal indicative of an analog input signal, the analog output signal varying, on-scale, between a scale maximum value and a scale minimum value; comparing, on the process variable transmitter, a first signal value indicative of the analog output signal with a second signal level indicative of the analog input signal to detect on-scale errors in the analog output signal. - View Dependent Claims (12, 13, 14, 15, 16, 17)
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18. A process variable transmitter, comprising:
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a processor that outputs a digital sensor signal indicative of a value of a sensor input signal; a digital-to-analog (D/A) converter that receives the digital sensor signal and provides an analog sensor voltage indicative of the digital sensor signal; a loop control component that controls current on a two-wire process control loop to vary, on-scale, between a scale maximum current and a scale minimum current, based on the analog sensor voltage, the loop control component regulating the current on the two-wire process control loop based on a regulation voltage across a resistive element in the two-wire process control loop; and a circuit that scales at least one of the regulation voltage and the analog sensor voltage so, when operating correctly, they have substantially a same magnitude, and compares the regulation voltage and the analog sensor voltage and outputs an error indicator if they differ by more than a threshold amount. - View Dependent Claims (19, 20)
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Specification