Typical Industry Low Level Signal Sensors
Most data loggers use a continuously varying electrical signal (analogue voltage) to send data from the sensor to the recorder. This is generally a low level signal where fewer than five volts represents the full scale (say a 100 degrees Celsius range) and therefore one tenth of a degree Celsius is only one two hundredth of a volt.
Achieving reliability in a laboratory environment with such a small signal is not generally difficult. However, it can be a major problem at a remote site with on-site staff installers, in harsh environments, and where equipment is expected to be reliable for upwards of ten years with a minimum of servicing.
In the field, the electrical signal can be easily degraded by nearby electrical interference, by poor electrical connections, or by changes to the length of cables. These problems can be introduced over time by electrical storms, by corrosion and by on-site staff, respectively.
Moreover, most analogue sensor types, such as a platinum temperature sensor, are individually calibrated. This individual calibration information has to be programmed into the recorder for the result to be accurate. This generally requires a technical person to install and if necessary, exchange sensors.
Environdata’s Digital Sensors
Environdata uses its own unique method of communicating between its sensors and its Weather Recorders.
Originally championed by Australia’s premier scientific body, CSIRO, the sensor sends a continuous square wave or series of pulses, where the pulse rate is proportional to the signal being sensed, and changes its rate with instantaneous changes in that signal.
The weather recorder then counts the pulses to provide an average value for the period being sampled. Note that the recorder detects the presence or absence of a pulse and not the size of the pulse.
Robust and Reliable Signals
Environdata uses five volt pulses as its signal so that, even in less than ideal conditions, the recorder will easily identify the pulses. In fact, with a five volt pulse, even one whole volt of electrical noise or contact resistance or cable loss will still result in a reliable signal (count of the pulses). (Compare this with the previous example where an analogue signal of one volt represents twenty degrees).
Each Environdata sensor incorporates its own signal conditioner that converts the low level signal sensed into five volt pulses. Further to this, each signal conditioner is calibrated to compensate for changes in the calibration of the sensing element.
The result is that all Environdata sensors of a particular model are directly interchangeable, without the need to alter any programming in the weather recorder. This makes field replacement by on-site staff reliable and easy to do.
Easy and Reliable to Test
Environdata’s sensors are easier to test because a simple test box (available from Environdata) will show if pulses are being sent or not. Measurement of analogue voltages and investigating cable signal losses are never required.
True Signal Representation
The Environdata sensors continuously respond to the sensing element by changing their pulse rate. This means the recorder receives a true average of the signal over the sampling period and enhances the reliability of the data recorded.
Increase of Resolution with Time
Whereas the analogue sensing method cannot provide an improved resolution over time, Environdata’s pulse counting method does result in better resolution as the counts increase over a longer period (10 minutes, one hour or even daily).
Easy to add new Sensors
Environdata’s Weather Recorders consist of a number of equivalent pulse counting channels. This means any combination of extra sensors can be added (provided there were enough inputs allowed for originally) or any combination of sensors can be re-configured.
In general, Environdata’s sensor methods result in more reliable signals and better recorded data. Environdata systems are more easily maintained, even in harsh environments, and this can be done by less technical personnel.