Signal transmission device for pulse density modulated signals

Abstract

A signal transmission device for pulse density modulated signals comprises a signal input for an input signal with a defined maximum signal value, a modulation stage for generating a pulse density modulated transmission signal out of the input signal, a locking device at the input for the pulse density modulated transmission signal to overwrite same with a static fault signal, a pulse reconstructing transmission path for the pulse density modulated transmission signal, a demodulation stage at the output, for reconstructing the input signal out of the transmitted pulse density modulated transmission signal, and a signal change monitoring device capturing the pulse density modulated transmission signal of the transmission path at the output, which has an error signal output for signaling the detection of a missing dynamic pulse density modulated transmission signal on the transmission path due to the static fault signal.

Claims

1-12. (canceled)

13. A signal transmission device for pulse density modulated signals, comprising a signal input (1) for an input signal (U.sub.E) with a defined maximum signal value (U.sub.Emax), a modulation stage (3) at the input side for the generation of a pulse density modulated transmission signal (U.sub.PWM) out of the input signal (U.sub.E), wherein the input modulation range (U.sub.R) of the modulation stage (3) at the input side is higher by a difference signal value () than the limited maximum signal value (U.sub.Emax) of the input signal (U.sub.E), a locking device (4), arranged downstream of the modulation stage (3) at the input side, for the pulse density modulated transmission signal (U.sub.PWM), in order to overwrite same with a static fault signal (U.sub.STAT), a pulse reconstructing transmission path (8) for the pulse density modulated transmission signal (U.sub.PWM), a demodulation stage (9) at the output side, for the reconstruction of the input signal (U.sub.E) out of the transmitted pulse density modulated transmission signal (U.sub.PWM), a signal change monitoring device (10) capturing the pulse density modulated transmission signal (U.sub.PWM) of the transmission path (8) at the output of same, which has an error signal output (11) for signaling the detection of a missing dynamic pulse density modulated transmission signal (U.sub.PWM) on the transmission path (8) due to the static fault signal (U.sub.STAT).

14. The signal transmission device according to claim 13, comprising an amplitude limiter (2) arranged at the input side to limit the analog input signal (U.sub.E) to the maximum signal value (U.sub.Emax).

15. The signal transmission device according to claim 13, wherein the modulation stage (3) arranged at the input side and the demodulation stage (9) arranged at the output side are configured for processing pulse density modulated or Sigma-Delta modulated transmission signals (U.sub.PWM).

16. The signal transmission device according to claim 13, wherein the locking device (4) is configured as a logic gate for generating a static high or low signal as a fault signal (U.sub.STAT).

17. The signal transmission device according to claim 13, wherein the locking device (4) can be activated by a monitoring device (7).

18. The signal transmission device according to claim 13, wherein the locking device (4) can be activated by a monitoring device (7) which is controlled by a micro controller.

19. The signal transmission device according to claim 13, wherein the pulse reconstructing transmission path (8) is configured by a galvanically isolated pulse transformer.

20. The signal transmission device according to claim 13, wherein the pulse reconstructing transmission path (8) is configured by a high voltage pulse transformer.

21. The signal transmission device according to claim 13, wherein the signal change monitoring device (10) is configured as retriggerable monoflop.

22. The signal transmission device according to claim 13, wherein the signal change monitoring device (10) is configured by an alternating voltage coupling of the transmission signal by means of a capacitor and (one way) rectification via a diode and a charging capacitor, wherein a parallel connection of a resistor towards the charging capacitor is provided for the implementation of a time constant of the monitoring device.

23. The signal transmission device according to claim 13, wherein a binary error signal (S.sub.F) is available at the error signal output (11) of the signal change monitoring device (10).

24. The signal transmission device according to claim 23, wherein the binary error signal (S.sub.F) is configured for actuating an error display (12) or for being transmitted to a monitoring and signal processing device arranged downstream.

25. The signal transmission device according to claim 23, wherein the binary error signal (S.sub.F) is configured for actuating an optical error display (12) or for being transmitted to a monitoring and signal processing device arranged downstream.

26. The signal transmission device according to claim 13, wherein the error signal output (11) of the signal change monitoring device (10) is coupled with a failure indication device (13), which can be activated by the error signal (S.sub.F), for generating a defined error message signal (I.sub.F) at the output side of the signal transmission.

27. The signal transmission device according to claim 13, wherein the error signal output (11) of the signal change monitoring device (10) is coupled with a failure indication device (13), which can be activated by the error signal (S.sub.F), for generating a standardized error message signal (I.sub.F) at the output side of the signal transmission.

28. The signal transmission device according to claim 27, wherein the standardized error message signal is a current signal (I.sub.F) of 0 mA in a 4 . . . 20 mA Live-Zero standardized signal transmission device or of 28 mA in a 20 mA standardized signal transmission device.

Description

BRIEF DESCRIPTION OF THE FIGURE

[0028] FIG. 1 shows a block diagram of a signal transmission device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] As can be seen from the drawing, the signal transmission device has a signal input 1, via which an input signal U.sub.E to be transmitted is input. Downstream of the signal input 1, an amplitude limiter 2 is arranged, which ensures that the input signal U.sub.E is limited for the further processing in the circuit to a maximum signal value U.sub.Emax, which is smaller by a difference signal value U than the maximum modulation signal value U.sub.R of a modulation stage 3 arranged downstream of the amplitude limiter 2 at the input side. Thus, it is provided that:

|U.sub.Emax||+/(U.sub.RU)|

[0030] The modulation stage 3, for example, in a common manner generates a pulse width modulated (PWM) square wave transmission signal U.sub.PWM out of the input signal U.sub.E. Due to the signal processing before the modulation stage 3, therefore, it is ensured during the regular operation that the dynamic PWM transmission signal U.sub.PWM, via the maximum modulation range of the input signal U.sub.EU.sub.Emax has a duty ratio differing from 0% or 100%, i.e. for example of 10% to 90%.

[0031] The modulation stage 3 is followed by a locking device 4, which can be a simple CMOS logic gate. One input 5 of same is connected with the modulation stage 3, whereas the second input 6 is coupled with a C controlled monitoring device 7. Due to this, at its output, either the PWM transmission signal U.sub.PWM for the error-free normal operation or a static fault signal U.sub.STAT, for example in the form of a logical 0, can be output in case the monitoring device 7, in its function as a watchdog circuit at the input side of the signal transmission device, has detected an error on the monitored circuit parts or with itself.

[0032] The locking device 4 is then followed by the actual pulse reconstructing transmission path 8, which, in the form of a high voltage isolation amplifier, transmits the PWM transmission signal U.sub.PWM in galvanically isolated form to the output side of the signal transmission device, for example by an inductive pulse transmission. There, it is available as a transmission signal U.sub.PWM, out of which in the demodulation stage 9 arranged downstream, the output signal U.sub.A corresponding to the input signal U.sub.E is reconstructed in a common manner

[0033] For the detection of an error state signalized from the input side, the PWM transmission signal U.sub.PWM at the output side is monitored by a signal change monitoring device, which in the embodiment shown is a retriggerable monoflop. This monitoring device 10 captures whether it is the dynamic PWM transmission signal U.sub.PWM which is pending or whether it is a static state of stress corresponding to the static fault signal U.sub.STAT. In the latter case, due to the missing dynamic PWM transmission signals U.sub.PWM, a corresponding binary error signal S.sub.F is output at an error signal output 11 of the monitoring device 10, with the help of which, for example, an LED warning light 12 is actuated and thus it is signalized that no regular input signals U.sub.E are transmitted, but that there is a fault state.

[0034] The binary error signal S.sub.Fas it is not shown in further detailcan also be processed further in a monitoring and signal processing device arranged downstream.

[0035] For the integration of this error message in a common industrial measuring environment, in the embodiment shown in FIG. 1, a failure indication device 13 is provided, which can be activated by the signal change monitoring device 10 with the help of its error signal S.sub.F. This is indicated by dashed lines in the drawing. As soon as such an error signal S.sub.F is pending, an error current signal I.sub.F of 0 mA is applied at a message output 14 of the failure indication device 13, which can be further processed in an analog manner in a standardized 4 . . . 20 mA-Live-Zero standardized signal transmission device, not shown in further detail.

[0036] Summing up, the present arrangement allows for the monitoring of circuit parts and micro controllers as well as for the provision of an error signal without the aid of a (further) micro controller and without a further electrically isolating signal transmission path, which is undesirable in a high voltage isolation amplifier, since it generally increases the failure probability as well as downgrades the interference resistance/EMC resistance and similar electronic parameters by parasitic effects, such as for example additional parasitic capacities, considerably.