Sensors
The MIDAS WTR is fitted with a choice of strain gauge or high accuracy
piezo-resistive pressure sensors, and a fast response PRT temperature
sensor as standard. Note that whilst the piezo-resistive sensor offers a
higher absolute accuracy, the quality of wave data owes more to
deployment location and sampling pattern than to sensor performance.
Optional additional sensors include Conductivity and Turbidity
Data Acquisition
In order to correctly measure wave activity, Linear Wave Theory requires a
specific number of data points to be sampled over a period of time. These
data points are then processed on board the instrument to generate an
accurate summary of the wave activity during the measured period. The
MIDAS WTR therefore operates in a strict pattern of “sample, process,
sleep”, with the user controlling the number of samples and the sampling
rate, together with the duration of the sleep period. This may be minimised
for almost continuous sampling, but obviously at the expense of battery and
memory usage.
Sample Rate: 1, 2, 4 or 8Hz.
No of Samples: Powers of 2, 128 - 4096 (more samples = better data)
Cycle Time: Minimum cycle time is nearest whole number of
minutes after processing has finished.
Delay Start: Instrument can be programmed to begin sampling at a
specific time.
Conditional: Wave Sampling only occurs if pressure activity exceeds
a defined level.
Memory
The MIDAS WTR is fitted with 64Mb solid state non-volatile FLASH memory.
Total capacity depends on setup. User may save any or all of the following:
Raw sensor data from each burst
Summary statistics of wave burst
Tide & additional sensor data
Spectral analysis of wave burst.
If all data is saved, memory will typically record over 4000 data bursts.
Sampling once per hour, this is over 5 months data.
Electrical
Internal: 32 x D cells, 1.5v alkaline or 3.6v lithium
External: 9 - 30vDC
Power: 0.7W (sampling), <1mW (sleeping)
Battery Life: Depends on sampling setup, typically:
>2 months operation (alkaline)
>5 months operation (lithium)
Communications
The instrument will operate autonomously, with setup and data
extraction performed by direct communications with PC before and after
deployment. It also operates in real time, with a choice of
communication protocols for a variety of cable lengths, all fitted as
standard and selected by pin choice on the output connector:
Standard
RS232 Up to 200m cable, direct to serial port via USB
adaptor
RS485 Up to 1000m cable, addressable half duplex
comms
Options
FSK 2 wire power & comms up to 6000m cable
Baud Rate: 2400 - 115200 (FSK fixed at 38400, USB 460800)
Protocol: 8 data bits, 1 stop bit, No parity, No flow control
Physical
Materials: Acetal housing, optional stainless steel (316)
seabed deployment frame
Depth Rating: Housing rated to 500m
Note: pressure sensor may be less
Size: 300mmØ x 290mm deep
Weight: 12Kg
Frame Size: 950 x 950 x 400mm
Frame Weight: 35Kg
