Power Management
The data acquisition applications in which the radio communication facilities of the Etherlog 3000 will prove most useful are those where the logger is inaccessible and frequent visits to collect data or change batteries are not feasible. In these situations the system must run for as long as possible from its internal battery. To achieve this goal the logger incorporates sophisticated power management techniques.Power management features
The Etherlog 3000 incorporates a range of features which allow battery life to be maximised:- the logger 'sleeps' between data acquisition and communication tasks. In sleep mode current consumption is typically only 40 microamps
- sensors may be energised immediately prior to taking a reading, and then powered down again to save battery life
- data may be gathered at selected times of day by 'windowing' acquisition tasks, saving power and at the same time data storage space
- the radio communication protocol is designed to ensure that the radio transmitter and receiver are energised for the least possible time
- radio communication can be windowed to occur only at selected periods during the day, for rapid response when required and minimum power consumption at other times.
Power management in action
The proof of our power management facilities is in the performance achieved. An Etherlog 3000 was used to carry out a typical data acquisition task:- measure eight analogue values at five minute intervals, one of which was the logger's own battery voltage
- store all eight values in the logger filing system
- window radio operation to guarantee a rapid connection to the logger during working hours and conserve power at other times
- download data from the logger every day
The battery pack supplied with the boxed Etherlog 3000 has a capacity approximately eight times that of the PP3 used in this test. On the logging task described it would have a life of approximately two years.
Unlimited battery life - using solar power
Some applications may require unattended data acquisition over extended periods,
or may need to use power-hungry sensors or a GSM modem. In these situations conventional
batteries may require frequent replacement, which can be inconvenient and
costly.
In these applications the very modest power requirement of the logger means that it can easily be powered from a small array of solar cells. The power management features remain invaluable, allowing the size of the photo-voltaic array to be kept to a minimum.
The solar panels are shown powering the Ethermet weather station, which has the GSM modem option fitted. A small sealed lead-acid battery provides the peak currents required by the GSM module, and its capacity is calculated to cover power requirements during the winter when hours of sunlight are at a minimum.