Portable autonomous device for the detection and recording of randomly occurring phenomena of short duration

The device of the invention uses at least one measurement chain comprising a sensor sensitive to the magnitude that one wishes to monitor, an analog-to-digital converter capable of supplying a digital signal representative of said magnitude, a microcontroller adapted for taking samples of said digital signal, of associating them with information enabling them to be time-stamped and of memorizing them in a memory that can be accessed by a read module, a logic reactivation circuit making it possible to command an operating period of the microcomputer when the sensor emits a signal announcing the occurrence of a monitored phenomenon. The invention applies particularly to the detection and recording of shocks which may affect goods during transportation thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a portable autonomous device for the detection 
and recording, during relatively long periods of time, of magnitudes 
representative of randomly occurring phenomena of short duration. 
It applies notably, but not exclusively, to the detection and recording of 
shocks capable of affecting objects such as goods, during transportation 
and/or handling thereof. 
Of course, such a detection can notably serve to subsequently reveal the 
cause of a deterioration of the object monitored and the moment (time 
stamping) at which the shock that caused this deterioration occurred. This 
information enables e.g. determination of who is responsible for the 
damage thus caused and can therefore constitute elements that are 
particularly useful to insurance companies, or even to the law. 
It is clear that within the scope of such an application, a device of this 
type must have considerable autonomy, while having as small a bulk as 
possible. Moreover, it must be perfectly tight, shock-resistant and be 
capable of operating under difficult conditions (high and low 
temperatures). It must also be completely inviolable (the memorized 
information must only be read by autorized persons and must be protected 
against all forms of destruction). 
2. Description of the Prior Art 
Given these imperatives, continuous detection of the magnitude to be 
monitored and periodical memorizing of samples representative of this 
magnitude are excluded. In fact, the power consumption specific to this 
type of operating is relatively high and does not enable both good 
autonomy and a low volume to be obtained. 
This is due to the fact that even in the case where one has, for the 
detection of the magnitudes to be measured, sensors that consume little 
electrical power (such as e.g. the capacitive accelerometers used for the 
detection of the shocks), the microcontroller necessarily used to ensure 
the operating sequences consumes too much electricity when operated 
continuously. 
With a view to solving this problem, the invention works from the 
observation that in the applications concerned by the invention, the 
phenomena to be detected: 
do not occur frequently (in theory, they should not occur at all), 
occur during a relatively short though not inconsiderable period of time. 
OBJECT OF THE INVENTION 
The invention thus puts these characteristics to good account and therefore 
proposes a portable measurement device using at least one sensor sensitive 
to the magnitude that one wishes to monitor, one analog-to-digital 
converter capable of supplying a digital signal representative of the 
magnitude detected by the sensor, a microcontroller capable of taking 
samples of said digital signal, of associating them with information 
enabling them to be time-stamped and to be memorized in a memory 
accessible by a separate read module of said device by means of suitable 
communications means. 
SUMMARY OF THE INVENTION 
Accordingly, a device therein comprises a logic reactivation circuit 
capable of commanding an operating period of the microcontroller when the 
above-mentioned sensor emits a signal announcing the occurrence of a 
monitored phenomenon. 
According to another feature of the invention, the microcontroller is also 
periodically reactivated for a time count, in order to enable 
time-stamping of the samples memorized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The device illustrated by these figures is more particularly intended for 
the detection and recording of the shocks undergone by a goods 
transportation vehicle, such as, e.g., a goods train wagon. 
This device comprises, housed in a box (block 1), which is preferably 
tight, shock-resistant and preferably flame-retarding, two measurement 
chains 2, 3, managed by a microcontroller 4 associated with a memory 5 and 
receiving a clock signal coming from a separate clock circuit 6. 
The first measurement chain comprises an accelerometer 7, preferably of the 
capacitive type, having a pendulum-type structure micromachined in a thin 
monocrystalline plate and capable of detecting accelerations of the order 
of .+-.25 g. 
This accelerometer 7 is angled so as to detect the horizontal, longitudinal 
component of the shocks to which the vehicle is subjected. Of course, this 
accelerometer 7 is associated with a conditioner 8 of the conventional 
type which supplies an analog signal filtered successively by a low-pass 
filter 9 (having e.g. a cut-off frequency Fe of 40 Hz with an attenuation 
of 24 dB/octave) and a high-pass filter 10 (having e.g. a cut-off 
frequency of 0.1 Hz and an attenuation of 6 dB/octave). 
The analog signal filtered at output of the high-pass filter 10 is 
transmitted, on the one hand, to an analog-to-digital converter 11 and, on 
the other hand, to a comparator with a window 12 delimited by an upper 
threshold and a lower threshold of e.g. .+-.1 g. 
This threshold comparator 12 produces for each of the acceleration values 
included in the .+-.1 g window, an inhibition signal which is applied to 
the converter 11 while making it inactive. 
In addition to its input connected to the filter 10, the converter 11 
comprises a clock input connected to a clock output P.sub.2 of the 
microcontroller 4, a serial port supplying eight-bit words (seven data 
bits and one sign bit) and connected to a data input P.sub.3 of the 
microcontroller 4 and an output for the purpose of transmitting an 
end-of-conversion signal to the microcontroller (port P.sub.1). 
Similarly, the second measurement chain 3 comprises an accelerometric 
sensor 13, also of the capacitive type, angled so as to detect the 
vertical components of the accelerations of the vehicle. This involves 
detecting whether or not the vehicle is moving. This accelerometric sensor 
13, which is intended to detect lesser accelerations (.+-.2 g), is also 
associated with a conditioner 14 of which the output is connected to a 
converter 15 capable of measuring the virtual value of the acceleration 
detected, by means of two successive filters, i.e. a low-pass filter 16 
having e.g. a cut-off frequency of 1000 Hz with an attenuation of 12 
dB/octave and a high-pass filter 17 having a cut-off frequency of 30 Hz 
with an attenuation of 6 dB/octave. 
The virtual value of the acceleration, determined by the converter 15, is 
applied to one of the two inputs of a comparator 18 of which the second 
input is connected to an output 3 of the microcontroller 4 which provides 
a threshold value (e.g. included between 0.01 g and 0.08 g) that can be 
selected by the microcontroller 4 (e.g. over three bits). 
The output of this comparator 18 is applied to a logic memorizing circuit 
19, also connected to the output of the comparator 12. 
This logic circuit 19 carries out a sampling-blocking, at regular 
intervals, of the status of the output of the comparator 18. It is 
inhibited upon detection of a shock by a signal coming from the comparator 
12. 
The sequencing of the microcontroller 4 and of its auxiliary units is 
ensured by means of a clock comprising a quartz oscillator 20-21 of which 
the output, which in this instance supplies a 2.097.152 MHz frequency 
signal, is applied to a reactivation circuit 22 of the microcontroller 4 
and to a frequency dividing circuit 23 which supplies, to a first output 
S.sub.1, a clock signal having a period of 1 mn and, to a second output 
S.sub.2, a clock signal having a period of 1 s. 
The 1-mn clock signal is applieed to one of the three inputs of an OR gate, 
24, while the 1-s clock signal is applied to the logic memorizing and 
updating circuit 19. The output of the OR gate 24 is connected to a 
control input of the logic circuit 22 which is connected by another input 
to an output P.sub.8 of the microcontroller 4 destined to supply a stop 
signal and comprises an output connected to a clock input P.sub.7 of the 
microcontroller 4 capable of receiving the clock signal produced by the 
oscillator 20-21, an output capable of supplying a control signal of a 
reference voltage generator 26 connected to the microcontroller 4 (port 
P.sub.9) and a watchdog output connected to a resetting input (port 
P.sub.10) of the microcontroller 4. 
The operating of the previsously described circuit is then as follows: 
The quartz oscillator 20-21 operates permanently. It has been specially 
researched for this application and is integrated in the dividing circuit 
23, the OR circuit 24 and the reactivation circuit 22, in an ASIC. Its 
consumption is very low (a few microamperes). 
The reactivation circuit 22 is designed so that the output frequency of 
this oscillator 20-21 is only supplied as clock frequency to the 
microcontroller during each of its periods of activity according to the 
process that will be disclosed hereinafter. 
The rest of the time, this frequency does not leave the ASIC in order to 
reduce the consumption of the unit (for indicative purposes, it should be 
noted that the stray capacity of an integrated circuit prong subjected to 
a frequency of 2 MHz under 5 V consumes a current of approximately 10 
.mu.A). 
Likewise, the two measurement chains 2, 3 operate permanently. Given the 
fact that the accelerometers 7, 13 used are of the capacitive type, the 
power consumed by these measurement chains 2, 3 is extremely low. 
In the absence of shock, the acceleration signal coming from the sensor 7 
remains within the window so that the comparator 12 transmits an 
inhibition signal which blocks the analog-to-digital converter 11, the 
memorizing logic 19 then being activated, and which interrupts the supply 
of reference voltage (block 26) to the microcontroller 4 and the 
transmission to the latter (port P.sub.7) of the 2.097.152 MHz clock 
signal produced by the oscillator 20-21 (via the OR gate, 24 and the logic 
circuit 22). 
At the same time, the second measurement chain 3 detects, at output of the 
comparator 18, the stopped/moving status of the vehicle, while the 
memorizing logic 19 carries out its sampling-blocking. 
Periodically, the pulse of 1-mn period produced by the dividing circuit 
causes, via the OR circuit and the logic circuit, a furtive reactivation 
of the microcontroller and activation of the reference voltage source, for 
a time count. During this furtive reactivation, the clock signal, produced 
by the oscillator 20-21, is applied to the port P.sub.7. 
When a shock occurs that is translated by detection by the sensor 7 of an 
acceleration value situated outside of the window of the comparator 12, 
the latter transmits an activation signal which activates the 
analog-to-digital converter 11 and the reference voltage source 26, and 
activates, by means of the application of this signal to a reactivation 
input (port P.sub.4) of the microcontroller 4, the putting into operation 
of the latter. At the same time, the memorizing logic 19 is inhibited. 
The microcontroller 4 then performs a read cycle on the information present 
at output of the analog-to-digital converter 11 (amplitude of the shock) 
and at output of the logic circuit 19 (which indicates the stopped or 
moving status of the vehicle prior to the shock) and which memorizes this 
information, with an indication of the moment at which the shock occurred 
(by means of a reading of the time counter). 
When the microcontroller 4 has completed its processing cycle, it indicates 
this to the logic circuit 22 by transmitting an end-of-processing signal 
to the port P.sub.8. The logic circuit 22 then produces a given number of 
clock pulses (e.g. 250) before stopping the provision thereof. 
The entire device returns to the dormant status until a further shock or a 
further time count pulse occurs. 
This process is illustrated by the timing diagram represented in FIG. 3 in 
which the crenellated curve C.sub.1 corresponds to the signal A at output 
of the OR gate 24, curve C.sub.2 indicating the presence or absence of the 
clock signal at input P.sub.7 of the microcontroller 4 and curve C.sub.3 
being the curve of operation (on/off) of the microcontroller 4. 
A pulse of signal C.sub.1 generated subsequent to a shock can be seen to 
cause transmission of the clock signal to the microcontroller 4. At the 
same time, the latter switches to the ON status for the duration of a 
cycle. At the end of the cycle, the microcontroller 4 switches to the OFF 
status. The transmission of the clock signal then ceases after 250 pulses 
of clock. 
The reading of the memorized information by the read module is carried out 
by means of a reading device 30 to which the detection module may be 
connected, the connection then being made by means of a conventional 
connector 31, e.g. of type RS232. 
This communication could of course be set up remotely by means of a 
communication system using electromagnetic, optical, sound or ultrasonic 
waves represented in broken lines in FIG. 2. 
In the example represented in FIG. 4, the device comprises three 
measurement chains similar to the measurement chain 2 illustrated in FIG. 
1. 
Each of these chains 2, 2', 2" therefore comprises an accelerometer 7, 7', 
7", a conditioner 8, 8', 8", a low-pass filter 9, 9', 9", a high-pass 
filter 10, 10', 10", an analog-to-digital converter 11, 11', 11" and a 
window comparator 12, 12', 12". The accelerometers 7, 7', 7" are 
respectively sensitive along axes, X, Y, Z perpendicular to one another. 
This device also comprises a fourth measurement chain identical to chain 3 
represented in FIG. 1 and which comprises a sensor 13, a conditioner 14, 
high-pass and low-pass filters 16, 17, a virtual value computing cirucit 
15, a threshold comparator 18 and a logic memorizing circuit 19. 
Unlike the embodiment represented in FIG. 2, the outputs of the 
analog-to-digital converters 11, 11', 11" are not directly connected to 
the microcontroller but via a multiplexer MUX. 
As for the inhibition outputs of the window comparators 12, 12', 12", they 
are connected to the reactivating circuit 22 by means of an OR circuit 32 
separate from the OR circuit 24 contained in the ASIC A.sub.S and of which 
the output is connected to an inhibiting circuit of the analog-to-digital 
converters 11, 11', 11". This inhibiting circuit can include a flip-flop 
(not represented) which is reset by the microcontroller via the 
multiplexer MUX. 
The operation of this device is similar to that previously described, 
except that subsequent to reactivation of the microcontroller 4, the 
scanning of the measurement chains is performed sequentially by means of 
the multiplexer MUX. 
It should be stressed that due to the arrangements previously described and 
to the fact that the oscillator 20-21 operates permanently, though the 
clock signal it produces does not leave the ASIC A.sub.S outside of the 
reactivation period, a minimal consumption of the unit is obtained while 
enabling the microcontroller to be active within a few microseconds of 
detection of a shock.