1.1 SDI-12 Interface

Solinst 2-wire signals are converted to SDI-12 signals by the SPX Wellhead. The SDI-12 Connector Cable, plugged into the side of this Wellhead, has three wires which connect to an SDI-12 master. These wires are colour-coded according to Table 1-1.


For more information about the AquaVent logger, Wellheads and Vented Cables, see the Vented Dataloggers User Guide.

The bottom of the Wellhead connects to a AquaVent logger through a Vented Cable. The AquaVent logger contains a small battery, used only for memory and clock back-up. The Wellhead contains four user-replaceable 1.5 V AA lithium batteries that power the AquaVent logger.

The SDI-12 interface circuitry requires the +12V connection to be powered by customer equipment. The current draw from the 12 volt source normally peaks at several 10's of mA, but idles around 30 uA. Upon initial power-up, or after disconnecting from Levelogger PC Software, the Wellhead draws about 3 mA from the SDI-12 equipment, while waiting to connect to the SDI-12 network. After the first SDI-12 command is received, the Wellhead idles around 30 uA.

Wire Colour SDI-12 Function Connection
Red 12 Volt Line +12V DC at SDI-12 Master
Black Ground Line Ground at SDI-12 Master
White Serial Data Line SDI-12 Data at SDI-12 Master

Table 1-1 SDI-12 Interface Cable Wire Definitions


The communication settings for the SPX Wellhead hardware comply with the SDI-12 standard at 1200 baud, 1 start bit, 7 data bits, 1 parity bit (even parity), and 1 stop bit.

Technical Specifications
Standard Compliance: SDI-12 Protocol, Version 1.3, July 18, 2005, except 'A' command
Maximum Sample Rate: 1 SDI-12 sample every 3 seconds with AquaVent not logging.
+12V Input: 9.6VDC-16.0VDC
Supply Current: Normally peaks at several 10's of mA, but idles around 30 uA.
SDI-12 Connector Cable Length: 15 ft (4.5 m)
Maximum Vented Cable Length: 500 ft (150 m)
Wellhead Operating Temperature: -20ºC - 80ºC
Wellhead IP Rating: IP 64 (dust and splash resistant)

Table 1-2 SDI-12 Technical Specifications