Overview; Hardware - Geokon 8025 Instruction Manual

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1. OVERVIEW

The MICRO-800 Datalogger is designed to support the reading of a large number of Geokon
Vibrating Wire Instruments for various unattended data collection applications through the use of
an internal Geokon Model 8032 Multiplexer. Weatherproof packaging allows the unit to be
installed in field environments where inhospitable conditions prevail. The Nema 4X enclosure
also has a provision for locking to limit access to responsible field personnel.
A basic datalogging system consists of the Campbell Scientific CR800 datalogger, an internal
multiplexer and an External Multiplexer port. Multiplexers expand the system by increments of
16 or 32 channels depending on the instrument type and configuration. The standard model
8025-2 Micro-800 datalogger can support one internal Multiplexer and external Multiplexer. The
External Multiplexer port can also be used to Daisy chain up to eight Multiplexers (please see
8032 Manual for more information). The standard model 8025-4 and 8025-5 dataloggers are
identical to the model 8025-2, but are configured for 32 VW gages only (8025-4) or 32
Thermistors only (8025-5). The standard model 8025-3 Micro-800 datalogger can support two
internal 16 channel Multiplexers and has 32 cable entries.

2. HARDWARE

The controller portion of the MICRO-800 datalogger consists of a Campbell Scientific CR800
Measurement and Control Datalogger. To gain an understanding on the workings and
capabilities of the CR800 it is necessary to read the Overview section of the CR800 Operator's
Manual. The CR800 Operator's Manual is available as a pdf file on the Campbell Scientific
Resource CD supplied with the datalogger.
A Campbell Scientific AVW200 Vibrating Wire Interface provides the required excitation and
signal processing for the vibrating wire sensors connected to the Datalogger. The AVW200 uses
spectral analysis to find the resonant frequency of the Vibrating Wire Gage. The AVW200 is
also used to measure the thermistor used in Geokon's vibrating wire instruments. For complete
specifications of the AVW200 see the AVW200 Instruction Manual on the Campbell Scientific
Resource CD.
A dual-mode battery charging circuit board is used to provide the charging voltage for proper
maintenance of the installed lead acid battery. The circuit board contains fused protected
terminal blocks used to provide a nominal 12VDC supply for devices such as the CR800 and
Model 8032 Multiplexer board. In some cases a Solar Charge Regulator may be used in place of
the dual-mode charger.
The Model 8032 Multiplexer board expands the number of channels that can be read by the
MICRO-800 Datalogger. The channel switching is accomplished by mechanical relays mounted
on the underside of the circuit board and the transducer connections are accomplished by friction
locking terminals. Power, reset and clocking for the multiplexer are supplied by the MICRO-800.
The Model 8032 multiplexer can be configured for 16x4 or 32x2 channels depending on
application. Please see Appendix F for more information on the Geokon Model 8032
multiplexer.
A 12 volt, seven amp hour, lead acid battery is used to provide power for the datalogger. The
battery is provided to supply operating power for a limited period of time should the AC or solar
power, used to maintain the battery, be interrupted. Under normal operating conditions and
proper maintenance, the life expectancy of the battery is approximately five years.