Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
  • G08C19/00—Electric signal transmission systems
  • G08C19/02—Electric signal transmission systems in which the signal transmitted is magnitude of current or voltage

Definitions

• the present invention relates to digital transmitters, in particular a transmitter with a current signal, in which the measured value is thus output by regulating a signal current or a feed current.
• Digital transmitters are those that include at least one microprocessor for processing the measurement signals or for controlling internal functions. In safety-relevant applications in particular, it is necessary to be able to detect the failure of a transmitter or its components with a sufficiently high probability.
• NAMUR recommendation NE43 suggests that in the case of measuring devices with a measuring signal current in a band range between 4 and 20 mA, a device failure with an error signal current outside this band range, e.g. no more than 3.6 mA or at least 21 mA is signaled.
• the present invention has for its object to provide a digital transmitter that safely signals the failure of its microprocessor.
• the object is achieved according to the invention by the transmitter according to independent claim 1.
• the transmitter comprises a microprocessor with a reset input and a clock output for providing a periodic clock signal; a monitoring circuit with a clock input and a reset output; and a current controller for outputting a measurement signal current, which measurement signal current represents a measurement value in measurement operation in a first band range; and signals an error outside the first band range; in which
• the clock input of the monitoring circuit is connected to the clock output of the microprocessor, the reset input of the microprocessor is connected to the reset output of the monitoring circuit, in the event of failure of the clock signal at the reset output of the monitoring circuit, a reset signal is periodically output will, further
• the transmitter has a comparator circuit with a first input, which is connected via a low-pass filter to the reset output of the monitoring circuit, with a second input, to which a reference voltage is present, and with an output, which is connected to an input of the current regulator is, after repeated output of the reset signal, the voltage at the first input of the comparator circuit exceeds the reference voltage, so that at the output of the comparator there is an actuating signal which causes the current controller to output an error signal current outside the first band range.
• the first band range for the measurement signal current is for example 4 to 20 mA.
• the error signal current should be at least 21 mA or at most 3.6 mA.
• the fault signal current is regulated to 22 mA.
• the monitoring circuit can, for example, comprise a digital counter which counts from a start value and, when a limit value is exceeded or undershot, causes a reset signal to be output at the reset output.
• the counter is reset to its starting value both by each pulse of the clock signal of the microprocessor and by the reset signal of the monitoring circuit.
• the limit value is selected based on the counting speed of the counter and the clock frequency of the microprocessor such that the limit value is never under or exceeded when the clock signal is functioning. Furthermore, the limit value is selected so that after a reset signal is sent there is sufficient time to restart the microprocessor after a simple clock fault, so that the clock signal is output again at the output of the microprocessor before the limit value is reached. Therefore, a new reset signal is only output if a reset signal has not led to a successful reset in the expected time.
• the low-pass filter via which the output signal of the monitoring circuit is fed to the comparator circuit, comprises an RC element.
• the comparator circuit preferably comprises a first operational amplifier.
• the current regulator comprises two parallel current regulator circuits, of which the first current regulator circuit regulates the measurement signal current in the first band range and the second current regulator circuit regulates the fault signal current to a value outside the first band region.
• the second current regulator circuit can comprise a second operational amplifier, one input of which is connected to the output of the comparator circuit, and the output of which is connected to the base of a transistor, via which the fault signal current is set. It is currently preferred that the internal voltage supply for the second operational amplifier for regulating the error signal current takes place independently of the voltage supply for the current regulating circuit for regulating the measurement signal current. This ensures that the fault signal current can also be set if the voltage supply to the current regulator circuit for the measurement signal current has failed.
• the first current regulator circuit for regulating the measurement signal current can be constructed similarly to the second current regulator circuit, the transmitter comprising an ASIC in a currently preferred embodiment and parts of the first current regulator circuit being integrated in the ASIC.
• Fig. 3 an example of a current regulator for re-implementing the present invention.
• the circuit of a transmitter according to the invention shown in FIG. 1 comprises a microprocessor 1 with a reset input and a clock output or trigger output for providing a periodic clock signal, which is shown as curve a in FIG. 2. Furthermore, a current regulator 2 is provided, which regulates the feed current of the transmitter as a measurement signal current between 4 and 20 mA. In normal measuring operation, the current regulator 2 receives an actuating signal, which represents a measured value, from the microprocessor 1 and regulates the feed current to a value corresponding to the actuating signal.
• the transmitter further comprises monitoring circuit 3 with a clock input and a reset output, the signal of which is shown as curve b in FIG. 2.
• the reset output of the monitoring circuit remains at zero. If, however, the clock signal fails to appear, then a reset pulse is output at the reset output, which is repeated after a certain time if the reset was unsuccessful and the clock signal of the microprocessor continues to remain 1.
• the signal of the reset output is also fed via a low pass 5 to the input of a comparator 4 which comprises a first operational amplifier.
• the signal curve at the comparator input can be seen from curve c in FIG. 2. If the reset is unsuccessful, several reset pulses increase the voltage until the reference voltage at the reference input of the comparator 4 is exceeded.
• the voltage at the output of the comparator 4 is increased, and is output as a fault control signal to the current regulator 2, which now outputs the supply current to a fault signal current of, for example, 22 mA.
• the general course of the feed current is shown schematically in curve d in FIG. 2. Accordingly, the value of the supply current in normal measuring operation in the band is between 4 and 20 mA and is regulated to 22 mA after a brief undefined transition, which is indicated by the X in the curve.
• the current regulator 2 shown comprises two current regulator circuits connected in parallel, of which the first current regulator circuit regulates the measurement signal current in the first band region and the second current regulator circuit regulates the fault signal current to a value outside the first band region.
• Both current regulator circuits each essentially comprise a current regulating transistor 21, 25 whose base is connected to the output of an operational amplifier 22, 26, respectively.
• At the inputs of the operational amplifiers 22, 26 there is in each case a control voltage for regulating the measurement signal current or the error signal current.
• the output of the comparator 4 is connected to the second operational amplifier 26 of the second current regulator circuit 12 via a series resistor R2.
• the reference input of the second operational amplifier is grounded.
• the output of the comparator When the output of the comparator is also grounded, the output signal of the second operational amplifier is grounded and the second transistor 25 blocks.
• the comparator 4 if the clock of the microprocessor fails, the comparator 4 outputs a control signal Uv fault current, then the second operational amplifier 26 outputs a voltage which lowers the resistance of the second transistor 25, so that a current flows through the second transistor , which causes a total supply current of 22 mA.
• the resistance of the main electronics, which is supplied by the supply current, and which is not shown in detail here, is summarized in this illustration by the resistor 27 or R HE.
• the first current regulator circuit for regulating the measurement signal current is in principle constructed similarly to the second current regulator circuit, the transmitter comprising an ASIC 24 in the embodiment shown and the operational amplifier 22 of the first current regulator circuit being integrated in the ASIC 24.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Current Or Voltage (AREA)
• Arrangements For Transmission Of Measured Signals (AREA)
• Amplifiers (AREA)
• Continuous-Control Power Sources That Use Transistors (AREA)

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• 2004
  • 2004-04-19 DE DE102004019392A patent/DE102004019392A1/de not_active Withdrawn
• 2005
  • 2005-03-23 WO PCT/EP2005/051344 patent/WO2005101345A1/fr active IP Right Grant
  • 2005-03-23 AT AT05729510T patent/ATE370487T1/de not_active IP Right Cessation
  • 2005-03-23 CN CNB2005800118534A patent/CN100481147C/zh active Active
  • 2005-03-23 DE DE502005001258T patent/DE502005001258D1/de active Active
  • 2005-03-23 US US11/578,838 patent/US7928742B2/en active Active
  • 2005-03-23 EP EP05729510A patent/EP1738337B1/fr active Active

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