50°C with pre-mechanical (LED) alarm temperature
points 0°C, 2°C, 8°C, 10°C, 15°C, 25°C, and
documentation of the entry in the non-volatile
memory. Quantitative values of temperature
registered in the calendar view and in real time form
in temperature-time schedules are sent to a personal
computer using a special USB-device. The software
should allow recounting total affecting temperature
into heat calories.
The tag provides the following operation modes:
sleep mode – thermo-sensor is not active,
there is no registration and the tag is ready to
receive commands to turn on;
operating mode – thermo-sensor is active, the
tag powered by the starting device is working
in the recording mode. Registered data are
stored in non-volatile memory in encrypted
state and until reading the information is
stored in an inaccessible area of the memory;
LEDs triggering on 0°C, 2°C without counting
temperature calories.
The tag includes the following components
shown in Figure 2.
A battery is a “tablet” battery of any radius (or
custom manufactured to an arbitrary shape). The
type of battery is chosen by the expected drain of the
device and its lifetime. If a wireless channel is used,
and the tag is expected to function about 2-3 years, a
lithium element battery is applied.
Figure 2: A schematic diagram of the tag.
If only a wired interface is used and the tag
lifetime is about half a year, a less expensive NiCd
battery can be implemented. Alternatively, a super-
capacitor also can be applied. Typical battery
parameters are 1.6-3.3 V, 50 mA maximum output
current, 150 mAh. The battery parameters can be
sacrificed, for example, if a smaller tag is needed
(and other reduced parameters are acceptable, such
as fewer measurements per unit time).
Non-volatile memory is used to store a tag log of
the monitored conditions (temperature, humidity,
etc). The log typically contains:
tag serial number;
tag-related data (i.e., a tag activation time, tag
manufacturing date, etc.).
The log data entries can be, for example:
TIMESTAMP1 – SENSOR1 MEASURE1 –
SENSOR2 MEASURE1 … – SENSOR N
MEASURE1
TIMESTAMP2 – SENSOR1 MEASURE2 –
SENSOR2 MEASURE2 … – SENSOR N
MEASURE2
A microcontroller (MCU) is used to:
acquire data from the sensors;
store the data into non-volatile memory;
acquire data from non-volatile memory;
send data via data interface.
The non-volatile memory can be embedded into
the microcontroller.
Sensors can be an integrated circuit or other kind
of device, with digital or analog output that converts
any physical parameter (temperature, humidity,
pressure, etc.) into voltage (analog) or code (digital).
This can be a thermocouple (a temperature sensor
based on the Seebeck effect (Encyclopedia of
Physics, 1998)), a humidity sensor (capacitive,
resistive or any other type), a pH sensor of any kind
(based on potentiometer, ion-sensitive field-effect
transistor, or on any other principle), an
accelerometer and a gyroscope (such micro-
electromechanical systems, capacitive
accelerometers, etc.), etc.
The sensors measure the value with the required
accuracy and should stay alive under any possible
conditions during the transportation. The sensors can
be embedded into the microcontroller.
A data interface is a communication channel
between the tag and the devices around it. The data
interface can be either wired or wireless.
A wireless data interface allows for
communicating with the tag during the entire period
of delivery, sending commands, reprogramming the
tag, reading data, etc. It is very helpful for different
logistic operations. The whole shipment might be
thrown away, if the tag data shows that the required
environmental conditions had been seriously
violated.
The main disadvantage is that it consumes a lot
of battery power and it significantly increases the
cost of the device. A wired interface, on the other
hand, does not allow communicating with the tag
when it is “in the box.” It can only be activated,
placed with the goods, and checked to see what was
going on with the shipment when it is unpacked. The
advantage is that it is less expensive.
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