Operating Instructions

Table Of Contents

6 SDI-12-commands and responses

The OTT SVR 100 communicates using the physical RS-485 interface via the SDI-12 transfer protocol. In this technical

documentation, you will find a detailed description of the SDI-12 commands implemented in the SDI-12 transfer protocol.

Further information on the SDI-12 standard can be found in the document "SDI-12; A Serial-Digital Interface Standard for

Microprocessor-Based Sensors; Version 1.3" (see website "www.sdi-12.org").

All advanced, manufacturer-specific SDI-12 commands on the OTT SVR 100 begin with "O" for OTT. With these commands

t is possible to configure the OTT SVR 100, for example using the "SDI-12 transparent mode" on a data logger or with the

OTT USB/SDI-12 interface (accessory).

Conventions for measured value formats

p – Sign (+,–)

b – Figure (before the decimal point)

e – Figure (after the decimal point)

! – Ends a command

6.1 Overview of standard SDI-12 commands

! a! Acknowledgement active

! aI! Send identification

! aAb! Change sensor address

! ?! Query sensor address; factory setting: 0

! aM! Start measurement

! aD0! Send data

! aR0! Continuous measurement

! aMC! Start measurement and request CRC (Cyclic Redundancy Check)

! aC! Start concurrent measurement (simultaneous measurement with multiple sensors on one bus line)

! aCC! Start concurrent measurement and request CRC

! aV! Start system test

Advanced commands (manufacturer specific)

! aOAA<value>! Set internal filter type

aOAA! Read internal filter type

Factory setting: 1 ➝ Floating mean

! aOAB<value>! Set measuring sensitivity

aOAB! Read measuring sensitivity

Factory setting: 14

! aOAC<value>! Set filter length

aOAC! Read filter length

Factory setting: 1 ➝ internal filter deactivated

! aOSD<value>! Set flow direction filter

aOSD Read flow direction filter

Factory setting: 0 ➝ Flow direction filter deactivated; both flow directions are recorded

! aOSU<value>! Set unit for "flow velocity" measured values

aOSU Read unit for "flow velocity" measured values

Factory setting: 0 ➝ m/s