GB2232851A - A method for synchronous data transmission - Google Patents

Description

-I- A method for synchronous data transmission The invention relates to a

method f or transmitting data for application, particularly but not exclusively, in motor vehicles.

In applied measuring techniques, it is often an object to obtain measurement data from inaccessible objects. As an example, objects to be measured in rotating parts or even in the human body can be mentioned.

In many cases, the energy for such systems is supplied via a more or less loose transformer coupling in the LF range (up to, for example, 200 kHz), depending on the distance between transmitting and receiving coil which is given by geometric boundary conditions and by the energy consumption of the sensor electronics.

According to the present prior art, transmitting back the measurement data obtained by the sensors is difficult and cumbersome. one possibility is to use the radio-frequency range, that is the data are transmitted by radiating electromagnetic waves.

The other possibility is to use the same frequency range as for energy transmission, that is data transmission by means of an alternating magnetic field. However, the power of a data carrier frequency modulated in some way with the data, which is sent back f rom, the sensor electronics, is in most cases so low that filtering the low data signal amplitude out of the energy signal amplitude is very difficult.

The interfering transformer-type energy transmission is therefore frequently switched off for the time of the data transmission and the measuring electronics are fed from a short-time energy accumulator, for example a capacitor.

The present invention seeks to specify a data transmission method which eliminates existing transmission problems.

2 According to the present invention there is provided a method for the synchronous data transmission, from f ixed or moving parts in motor vehicles, wherein a loosely coupled transformer or rotary transformer, via which measuring electronics to be operated are supplied with energy, is loaded by the measuring electronics at the rate of a divider factor of the energy frequency, and this periodic loading is subject to a phase change with respect to the energy signal when the level of the binary data signal to be transmitted changes, the loading is transferred to the feeding voltage on the primary side of the transformer and, for the recovery of the data, is again multiplied by a periodic signal of the same divider f actor of the energy f requency, whereaf ter the result of the multiplication, af ter averaging, is supplied to a comparator at the output of Which the data signal is available again.

Preferably, the loading is effected with an arbitrary divider factor, for example, 1/2, 1/4 or 1/8 of the energy frequency, preferably half the energy frequency. - Preferably,the loading is effected at the rate of pseudo-statistical noise which is synchronous with the energy signal or its divider factors and the binary sequence of which is stored as fixed value in a storage component both on the primary and on the secondary side.

The frequency may be divided by means of flip flops. The loading may not be effected by the measuring electronics but by an additional load resistor.

The subject matter of the invention is a method for the simultaneous transmission of electric energy in the direction of the measuring electronics to be operated and of data in the other direction. The advantages lie, on the one hand, in the noise immunity of the data transmission and, on the other hand, in the fact that virtually no additional energy is needed for transmitting back the data.

The invention will now be described by way of 1-, 1 3 example with reference to the accompanying drawings in which: - Figure 1 shows the synchronous data transmission by adding the electronics load at half the energy frequency, Figure 2 shows the voltage curve, and Figure 3 shows the transmission back of data by adding the electronics load with a synchronous pseudostatistical noise.

The transmit coil Ll is f ed from the alternating voltage source U, at frequency fl. The coupling flux k passing through both coils L, and L2 induces the voltage U2 across L2 which can be increased further by the resonance capacitor CRes, depending on necessity.

If the electronic switch S is closed, the f ilter capacitor Cs is charged up to the direct voltage US via the diode' D at the rate of the frequency f. From this direct voltage, the following electronics are supplied with the current IE.

These electronics contain a flip flop which converts the frequency fl of the voltage U2 into a rectangular signal Uf2 having the frequency f2 = fl/2.

f2 is supplied to a connection of the exclusive-OR (or coincidence) gate used as modulator. The digital, serial data signal Data generated by the measuring electronics and to be transmitted is applied to the other input of the modulator. The baud rate of Data is distinctly less than the frequency f2 = fl/2.

The modulator has the function of a converter/inverter controlled by Data. The logical output signal UMOD Of the modulator is either equal to Uf 2 or equal to Uf 2, depending on whether Data = low or Data = high is true. UMOD is therefore rectangular and has the frequency f2 = fl/2 but, in this signal, a phase shift of +180() or -1800 occurs with a level change of Data. - UMOD is now used for controlling the switch S. The filter capacitor Cs is thus not recharged at the rate of the frequency fl present in front of the switch but now 4 only at the rate of the frequency f 2 = f 1/2. When Data changes level, this periodic recharging process is subjected to a phase change.

Thus, current or energy is taken from the coil L2 or the resonant circuit L2 r CRes only at the rate of f 2 = f 1/2 and, moreover, only during the positive half waves Of U2 because of the diode D.

This removal of current has the consequence that each second positive half wave Of U2 exhibits a dip.

Depending on the size of the transformer coupling, this signal variation is transmitted to the primary coil L,, that is to say the amplitude dips can also be seen in UL1, even if in a weakened f orm. This results in the signal variation of Figure 2.

The Fourier analysis of UL, results, in addition to the fundamental wave at frequency fl, in the data transmit frequency fl/2 and its harmonics.

For the recovery of the data, only the fundamental wave of the data transmit frequency ux = (AX COS 2 -i-r f 1/2 t and its phase relationship with respect to the feeding voltage U1 = L11 COS 2 71 f It is of interest.

When the signal Data to be transmitted changes its level at times t, and t2, the phase relationship between Ux and U, changes just as abruptly which, in turn, is equivalent to a sign change ofi7x.

Now, let 2 X Data = low < 0 Data = high=Lúx > 0.

For demodulating the data, the auxiliary voltage UH = VH cos 2 -lr f 1/2 t is first again obtained from U, by simple frequency division, with an amplitude H which is independent of 1 and constant. (In principle, a rectangular voltage of the same frequency is also possible). UH is always locked to U, in phase and also always has the same frequency as the Ux to be detected, namely precisely fj/2.

Demodulation is then achieved by electronically multiplying ULI, including the Ux contained therein, by the auxiliary voltage UH and subsequently averaging with respect to time (for example by means of a low-power filter). This provides the demodulated signal UDem " ULi UH - ax H- As can be seen, only the component having the same frequency as UH, namely only Ux, in UL1 contributes something to the average.

If the sign of LLH is constant, that is to say if, for example LtH "' 0 it finally follows that L,tx 4" 0 UDEM " 0 => Data low -4x > 0 => UDEM > 0 => Data high.

Data is then immediately available after a subsequent comparator.

The lower the Baud rate in relation to the frequency f2 = fj/2, the slower the averaging can be made and the narrower the bandwidth and greater the noise immunity of the data transmission.

A further decisive advantage of the method lies in the fact that no additional transmitting energy is needed for the data transmission but the special type of load modulation has the result that only the electronics to be operated themselves consume energy.

A refined variant of the data transmission is produced if the opening and closing of the switch S on the sensor electronics side is not controlled by a fj/2 but by a pseudo-statistical signal in the pattern of fj/2 (Figure 3). The pseudo-statistical signal is stored in a read-only memory (ROM) in the sensor electronics.

The 8-bit-long word WStat = 10011010 shall be assumed as an example. The succession of zeros and ones is selected arbitrarily.

If Data = high, the switch is driven at the rate of 6 the non-inverted l7Stat,. if Data = low, the switch is activated at the rate of the inverted signal WStat "'' 01100101 The amplitude dips in UL1 will then correspond.

For demodulation, the multiplier no longer needs to be driven at fl/2 but with the same pseudo-statistical signal WStat which is also used for modulating in the sensor electronics.

There is a certain effort associated with finding the correct phase angle for UH - WStat so that UDem also converges. However, this search algorithm can be easily achieved by means of an intelligent control system.

The outstanding advantage obtained by using a pseudo-statistical signal as modulation carrier is the insensitivity also to discrete noise frequencies.

Pos;ible applications for the method according to the invention are given, for example, in motor vehicles in checking the tyre pressure, the possibility of a locking system with identification card or the transmission of signals from the steering wheel. The data transmission for other sensors provided at moving or rotating parts is also conceivable.

Y t 7

Claims (1)

1. Claims:

   1. A method for the synchronous data transmission, f rom f ixed or moving parts in motor vehicles, wherein a loosely coupled transformer or rotary transformer, via which measuring electronics to be operated are supplied with energy, is loaded by the measuring electronics at the rate of a divider factor of the energy frequency, and this periodic loading is subject to a phase change with respect to the energy signal when the level of the binary data signal to be transmitted changes, the loading is transferred to the feeding voltage on the primary side of the transf ormer and, for the recovery of the data, is again multiplied by a periodic signal of the same divider factor of' the energy frequency, whereafter the result of the multiplication, after averaging, is supplied to a comparator at the output of which the data signal is available again.

   2. A method according to Claim 1, wherein the loading is effected with an arbitrary divider factor.

   3. A method according to Claim 2, wherein the divider factor is 1/2, 1/4 or 1/8 of the energy frequency.

   4. A method according to Claim 3 wherein, the divider factor is half the energy frequency.

   5. A method according to any one of the preceding Claims, wherein the loading is ef f ected at the rate of pseudo-statistical noise which is synchronous with the energy signal or its divider factors and the binary sequence of which is stored as f ixed value in a storage component both on the primary and on the secondary side.

   6. A method according to any one of Claims 1 to 5, wherein the frequency is divided by means of flip flops.

   8 7. A method according to any one of Claims 1 to 6, wherein the loading is not effected by the measuring electronics but by an additional load resistor.

   8. A method for the synchronous data transmission from fixed or moving parts in motor vehicles, substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

   z PubliShedI990atThe Patent Office, State House. 66'71 High Holborn, London WClR 4TP. Firther copies maybe obtained from The PatentOffice. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87