Texas Instruments | Efficient cold chain management with scalable temperature sensors | Application notes | Texas Instruments Efficient cold chain management with scalable temperature sensors Application notes

Texas Instruments Efficient cold chain management with scalable temperature sensors Application notes
Efficient cold chain management with scalable
temperature sensors
From producers to consumers, it is important that
perishable items, especially food and medicines, reach
the end consumer in fresh and viable condition, so as
to maintain their nutrients and efficacy. To ensure
quality and product safety, manufacturers specify the
temperatures at which the items must be transported
and stored.
Before reaching the consumer at their local grocery,
perishable produces like fruits, vegetables or frozen
meals, spend a significant time in transportation and
on the shelves of large refrigeration units as shown in
Figure 1. Thus it becomes crucial that these items be
maintained at the correct temperature.
Cold chain management and Good Distribution
Practices (GDP) ensures that the right conditions are
met during every phase of the life cycle of packaged
and perishable items. At the same time it ensures that
anytime a possible excursion outside the storage
temperature is about to occur, an appropriate action
can be taken by the operator either during
transportation or during storage to ensure that there is
as little wastage as possible.
As shown Figure 2 in the point to point topology, a
single microcontroller (MCU) is connected to a
temperature sensor that may be an analog output or a
digital output sensor. This is useful when managing a
pallet of goods during shipping.
Wireless Communication
Battery
+
_
MCU
Temperature Sensor
x
Data Logger
Figure 2. Point-to-Point Topology
However when sensing multiple locations like display
in refrigerators or in reefer containers, the cost of a
single MCU is too high to be implemented multiple
times in the entire system. In such cases, the most
common topologies that are used are the star, daisy
chain (Figure 3) or shared bus, with one MCU being
the host controller for multiple sensors. A star topology
allows easy fault isolation if one of the branch fails and
may use both analog and digital output temperature
sensor, but has a higher cost of implementation as the
controller peripheral count is higher because of which
the system cannot scale very well and the cost of
assembly and cable itself.
Figure 1. Typical Grocery Aisle
Cold Chain Topology
Use of temperature sensors with gauges and simple
analog sensors, have been quite common for a long
time. However, with advances in semiconductor
technology and the fact that most cold chain
management is done in the temperature range of
–40°C to +10°C, integrated temperature sensors are
the best option for cold chain management in these
temperature ranges. Based on the application, there
are different topologies that may be deployed.
SNOAA33 – March 2019
Submit Documentation Feedback
On the other hand, with shared bus, the scalability can
easily be addressed with digital temperature sensor
that share the line and may be individually addresses
using in band addressing like the case of I2C bus or
out of band signaling using chip select which is the
case with SPI. However, reliable power delivery and
signal integrity over a long chain may be a concern.
The daisy chain does not require out of band signaling
and rather uses in band addressing scheme. As each
stage of the chain acts as a buffer for the next chain,
signal integrity may be maintained over longer
distances.
Efficient cold chain management with scalable temperature sensors
Copyright © 2019, Texas Instruments Incorporated
1
www.ti.com
Wireless Communication
Battery
+
_
MCU
Temperature Sensor 1
Temperature Sensor 2
x
Data Logger
Temperature Sensor N
Figure 3. Daisy Chain of Temperature Sensors
Figure 4. Eye Diagram for TMP107
Irrespective of which stage of cold chain management
is being monitored, electronic systems provide a
unique advantage of not only logging the temperature
of the pallet or refrigeration unit, but also providing
thresholds that generate alert above a certain
threshold. Such events can be visually communicated
through audio or visual alerts like a buzzer of flashing
LED, but also can be integrated into cloud services
using both wired or wireless MCU, allowing round the
clock monitoring and data logging.
Daisy chain topology in cold chain management
The TMP107 is a digital output temperature sensor
that supports a total of 32 daisy-chained devices and
is ideal for replacing NTC thermistors in cold chain
management, because of its high accuracy and ease
of system wide scalability without the need to add
additional MCUs. The TMP107 has a maximum
accuracy specification of ±0.4°C in the range of –20°C
to +70°C and ±0.55°C in the range of –40°C to
+100°C with a temperature resolution of 0.015625°C.
With an automated address assignment, the TMP107
allows system developers to write software without the
need to assign the address at each sensor node as
the system is scaled by adding additional sensor node.
At the same time, with the use of a push-pull
communication IO, the system is made more resilient
against the noise affecting the temperature value over
long cables. This allows for data transfers over span
lengths of 1000 feet between adjacent devices in the
chain.
Figure 4 shows the signal integrity of the
communication interface at 9600 bps. The
communication interface of SMAART Wire™ uses
UART bus which is a standard peripheral on almost all
MCU, making it easier develop software, than using
bit-banged approach. At the same time, with a daisy
chain implementation, it makes it easier to identify the
location of a cable break, which enables easy
maintenance and overall system reliability.
2
The current consumption of the TMP107 when
performing temperature conversions with an active bus
communication is typically 300 µA. It has a shutdown
current of 3.8 µA in low power mode. With a wide
operating voltage of 1.7 to 5.5 V, the low current
consumption makes it ideal for battery operated
systems during transport phase of cold chain
management. At the same time the baud rate can be
increased for more real time update as may be the
case when storing frozen food items.
Additionally, TMP107 allows the configuration and
temperature limits to be stored to its internal nonvolatile memory. This enables the device to be autoconfigured on power up, eliminating the need for
individual device configuration to be performed making
the system operational faster. It also has 8 EEPROM
locations providing up to 128 bits of EEPROM to store
user information or calibration information.
In conclusion, the daisy chain topology is the best way
to implement an efficient cold chain temperature
monitoring. The TMP107 has the right combination of
accuracy, power consumption and features to support
a battery-based cold chain management system.
Table 1. Alternative Device Recommendations
Device
Optimized Parameters
Performance Trade-Off
TMP107
0.4°C accuracy and 32
devices in daisy chain
—
TMP144
Small form factor
16 devices in daisy chain
and 1°C accuracy
Efficient cold chain management with scalable temperature sensors
Copyright © 2019, Texas Instruments Incorporated
SNOAA33 – March 2019
Submit Documentation Feedback
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you
permission to use these resources only for development of an application that uses the TI products described in the resource. Other
reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third
party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims,
damages, costs, losses, and liabilities arising out of your use of these resources.
TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on
ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable
warranties or warranty disclaimers for TI products.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2019, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertising