Instruction manual

Appendix D. SDI-12 Sensor Support

D.1 SDI-12 Command Basics

SDI-12 commands have three components:

Sensor address (a) – a single character, and is the first character of the

command. CS650 sensors are usually assigned a default address of zero unless

option –VS is selected at the time of ordering. Sensors with the –VS option are

addressed with the last digit of the probe’s serial number. This allows for

multiple CS650’s to be connected to a single control port without requiring the

user to change the SDI-12 addresses from zero.

Command body (e.g., M1) – an upper case letter (the “command”) followed by

alphanumeric qualifiers.

Command termination (!) – an exclamation mark.

An active sensor responds to each command. Responses have several standard

forms and terminate with <CR><LF> (carriage return – line feed).

SDI-12 commands supported by the CS650 are listed in TABLE D-1.

Continuous and concurrent measurements are not supported.

TABLE D-1. CS650 SDI-12 Command and Response Set

Name Command Response

Acknowledge

Active

a! a<CR><LF>

Send Identification aI! allccccccccmmmmmmvvvxxx...xx<CR>

<LF>

Change Address aAb! b<CR><LF>

Address Query ?! a<CR><LF>

Start Measurement aM! atttn<CR><LF>

Send Data aD0!

aD1!

a<values><CR><LF>

Additional

Measurements

aM1!

aM2!

aM3!

atttn<CR><LF>

Address Query Command (?!)

Command ?! requests the address of the connected sensor. The sensor replies

to the query with the address, a.

Change Address Command (aAb!)

Sensor address is changed with command aAb!, where a is the current address

and b is the new address. For example, to change an address from 0 to 2, the

D-1