This article explains how to estimate the battery life of wireless sensors powered by batteries. Broadsens wireless vibration & temperature sensors have the best battery efficiency in the industry. Broadsens recommends using 80% of the battery capacity for the battery life estimate in room temperature, which is more realistic in applications due to temperature variation and battery depreciation. If a wireless vibration & temperature sensor works in a harsh environment , then we recommend using less than 60-70% of the battery capacity for more realistic estimate. Extreme cold temperature can reduce battery capacity significantly. For example, at -30 degree Celsius (-22 Fahrenheit), the battery capacity can reduce to only 25% of the nominal value.
User can use this battery life calculator to calculate the battery life based on current consumption.
1. SVT-A series wireless vibration & temperature sensors. There are many different DAQ modes and sample rate options of SVT-A series sensors. Each DAQ mode and sample rate has different power consumption. User can refer to section 2.5 of the “Wireless Gateway Operational Manual” for power consumption of each mode.
Example 1. In this example, we take data in real time mode at 50Hz sample rate, the average current is 180uA with data acquisition and transmission based on the vibration sensor system manual. The average idle current including heart beat is 22uA. Assume that user takes data for 2 minutes every hour. Therefore, for each hour, 2/60 time is taking data, and 58/60 time is idle. Then the average current of the sensor consumption is 22*58/60+180*2/60=27.27 uA. If we input 80% of SVT sensor’s battery capacity, which is 960mA, and enter 0.027mA for the power consumption, then we know that the SVT-A wireless vibration sensor battery can last more than 4 years if user takes data for two minutes every hour in real-time mode (50Hz sample rate).
Example 2. In this example, we use single DAQ mode at 6.4kHz sample rate. Because single DAQ mode guarantees that no data loss, if the signal is weak between the sensor and the gateway, or there exists strong interference, then the sensor will resend data which consume extra power. For simplicity, we assume that the signal quality is good and there is minimum data retransmission. Number of sample points also plays important role. The more data points we send, the more time and power consumption it will take. Let’s assume that we send 16,384 samples, which typically take 1 minute to sample and send the data to the gateway. If there are multiple SVT-A sensors in the same group, then all the sensors will share the bandwidth, which will take longer time to send the data. Typically the data transmission can be finished in less than 1 minute and 30 seconds if there are up to 6 sensors (assuming that the signal is good). We will use two minutes as the worst-case estimate. Based on the current consumption at single DAQ mode, the worst-case current is 600uA. We also assume that the sensors take data every hour. Then the average current of the SVT-A sensor can be obtained: 22*58/60+600*2/60=41.27uA.
Based on the battery life calculator, we know that the SVT-A wireless vibration sensor battery can last 2 years and 8 months.
However, if we only take 8,192 samples, then the data acquisition and transmission can be finished in 1 minute, and the average current is reduced to: 22*59/60+600*1/60=31.63uA.
Then the SVT-A sensor battery can last 3 years and 6 months, which is a huge difference.
Please note that the above estimate does not take into account signal strength and environment interference. If the signal is weak or there is strong interference, then in certain DAQ modes, SVT-A sensor will retransmit data to ensure data integrity. This can further reduce battery life.
2. SVT-V series wireless vibration sensors. It is easy to estimate the battery life of an SVT-V sensor. Section 3 of the system manual has an excellent battery life estimate for SVT-V series sensors. The battery life of SVT-V series sensors can last five years or more if the machine runs less than 8 hours a day in average. An advantage of SVT-V series sensor over SVT-A series sensor is the battery duration is not affected by signal interference, since SVT-V series sensors are true real time sensors, which will ignore data loss and send the new calculated results to avoid data accumulation.
3. SVT-LA series long-range wireless vibration sensors. The battery capacity of SVT-LA sensor is 4,000mA. The power consumption of SVT-LA series sensors is slightly higher than SVT-A series sensors. We recommend using 70%-80% of the battery duration of SVT-A series sensors for SVT-LA series sensors.
4. SVT-LV series long-range wireless vibration sensors. The battery capacity of SVT-LA sensor is 4,000mA. The power consumption of SVT-LA series sensors is slightly better than or comparable to SVT-V series sensors. We recommend using the same battery duration of SVT-V series sensors for SVT-LV series sensors.