Sensornet ORYX DTS, User Manual

Page: 71 / 101

Oryx DTS User Manual v4 Page 65
Click ‘Next’ to proceed.
Setting the Spatial Averaging & Measurement Time
The user is then prompted to set the spatial averaging and measurement time. The
spatial averaging does not affect the way the DTS takes measurements but simply
combines a certain number of adjacent measurement points into one data point by
calculating the mean of those temperature points. The effect of this is to reduce the
measurement noise (point-to-point variations) but reduces the spatial resolution
(smoothing of features along the fibre). The default value is the minimum spatial
averaging allowed by the system – no point-to-point averaging. This minimum
spatial resolution is determined by the pulse duration of the laser and the sampling
period of the data acquisition system.
The measurement time is the time taken to collect data, average the signals on-
board and transfer to on-board memory. During most of the measurement time, the
laser will be active and repeated firing (or triggers) of the laser are recorded. These
signals are averaged on-board to reduce the noise on the final temperature data
trace and improve the temperature resolution. Hence, longer measurement times
will reduce the noise and improve the signal-to-noise ratio.
NOTE: The noise reduction follows an inverse square-root law with measurement
time – i.e. to reduce the noise by a factor of 2; the measurement time needs to be
increased by a factor of 4.
For very short measurement times, <30s, a portion of the time is used for
transferring the data to memory. (The exact period of data transfer time depends on
the range selected).
It may be important to ensure the measurement time is short enough to capture any
thermal changes in the system being monitored but also, long enough to reduce the
noise to acceptable levels and resolve small temperature differences.
Further Channel setup
Following the spatial averaging and measurement time screen, the user is
prompted to configure other channels in a similar manner if required. If other
channels are not required, simply leave the channel de-activated.
Repetition Time & Number of Measurements
The next screen is where the user defines the repetition time and whether the DTS
should measure continuously, or record only a set number of measurements and
then stop (Figure 47).