SDI-12 Overview

SDI-12 Operation

The EasyQ includes both RS232 and SDI-12 interfaces. You set up the EasyQ through the RS232 port using our standard Windows EasyQ software. You can set the SDI-12 address when you tell the instrument to switch to SDI-12 mode.

Once in SDI-12 mode, you will communicate through the SDI-12 interface. The following two SDI-12 commands give you access to water velocity and stage separately:

0M! Velocity measurement
0M1! Stage measurement

The above assumes the EasyQ is set for address 0.

Velocity Data

Nine values are returned in both cases for an EZQ, for velocity these are:

X Velocity cell 1	(ft/s)
Y Velocity cell 1	(ft/s)
Amplitude cell 1	counts*100+counts
X Velocity cell 2	(ft/s)
Y Velocity cell 2	(ft/s)
Amplitude cell 2	counts*100+counts
X Velocity cell 3	(ft/s)
Y Velocity cell 3	(ft/s)
Amplitude cell 3	counts*100+counts

The amplitude data is in the form AABB where AA is the amplitude for beam 1 and BB is the amplitude for beam 2. The range for AA and BB is 0-99, each count corresponding to about 1.1 dB.

Stage Data

Nine values are returned for stage

Stage	(ft)
Quality	counts
Pressure	(ft)
Pitch	degrees
Roll	degrees
Stage(p)	(ft), based on pressure
Quality(p)	counts, based on pressure
%Good1
%Good2

Stage and Stage(p) both use acoustic stage measurement. Stage(p) is the preferred stage measurement becasue it uses the pressure to reject echoes from debris and out-of-range echoes. Stage (without using the pressure sensor) is included to provide a fallback in case the pressure sensor is defective or given the wrong offset. The stage quality is a measure of how well the echo conforms to the shape that is expected for the echo from a flat surface. %Good tells you the percentage of stage measurements that produced good stage values. Our observation thus far is that %Good as little as 1% is sufficient for a good reading, so you should reject stage values only when %Good = 0.