Temperature tracking in reefer trucks
We are currently working with a client to add wireless temperature sensing to their fleet of reefer trucks. WiSense wireless sensor nodes are a perfect fit for such applications. These nodes have a sleep mode current consumption of less than 2 micro-amps – vital for achieving long battery life. They operate in the license free 865-867 MHz ISM band which has a longer range and better penetration compared to the 2.4 GHz band. Whats more , the sub-Ghz band is virtually unused in India.
Reefer trucks are a vital component of any cold chain. These trucks have a refrigerated cargo unit to keep perishable goods such as fruits, vegetables, ice cream etc at the optimal temperature. I was talking to a group of reefer drivers near a cold storage facility in East Bangalore. This group had just delivered trucks full of Amul ice cream from Gujarat to Bangalore – a non stop journey of forty hours in the blistering heat of an Indian summer.
Here are some pics courtesy Eicher – a major supplier in India.
The solution required interfacing our coordinator/receiver node with a GPS/GPRS tracking device. The trucks are currently equipped with a wired temperature sensor. This sensor is installed near the AC inlet at the front of the container. The sensor is wired to the GPS/GPRS tracker inside the truck’s cab. This wiring is also making the solution unreliable, hence the move to a wireless link.
How does the system work ?
We have a high accuracy temperature sensor (with probe) connected to a WiSense WSN1120-P node. This node has an internal PCB antenna and is powered by a couple of AAA batteries. This sensor node can be installed outside the container with the sensor probe inserted into the container through a hole in the body. The other option is to install the whole node inside the container. If the Reefer container is a metal box, it will form a Faraday’s cage which can severely impact RF communication between a sensor node inside the container and the receiver in the truck’s cab. Having said that, reefer containers are not perfect Faraday cages. We placed our sub-GHz transmitter node inside the container. The coordinator/receiver node in the cab continued to receive packets from the sensor node although we did observe packets being dropped now and then. To avoid any reliability issues, it may be better to install the sensor nodes on the outside of the reefer container.
Our coordinator/receiver node is connected to a GPS/GPRS tracker device. We used an analog input on the tracker to forward temperature data received from our sensor node. The receiver node converts the temperature data in to an analog voltage signal using a DAC. This signal is converted in to a digital value by an ADC in the tracker unit and sent to the cloud. The cloud software converts this voltage value back in to temperature.
Here are some pics of the installation.
Here’s a snapshot of the sensor’s data visualized in the cloud.
For more information on WiSense products, please visit wisense.in