Introduction
•
Digitizing the data at source allows you to ensure that its origin can be
reliably traced.
•
The DM24 digitizer may also be combined with an Authentication Module
within the borehole sonde, allowing you to generate cryptographically-signed
data at the point of origin.
A digital borehole installation can be provided with RS232, RS422 or fibre-optic links
to the surface, depending on the depth of the borehole and the distance from the
well-head to the surface controller (i.e. the total cable length).
When a down-hole digitizer is present, it takes the place of the strain relief unit in
the borehole. The surface unit also takes a slightly different form, with a serial
connector allowing you to attach a modem or other communications link. In this
type of installation, instead of using the surface unit to pass control signals to the
sensor, all functions are accessed remotely via the digitizer.
If you prefer to install a stand-alone digitizer at the surface, it should be connected to
the 26-pin “RECORDER” socket of the breakout box.
2.3 The hole lock system
The hole lock clamp unit in a 3TB instrument provides a stable platform for the
sensor modules mounted above and below it. It is designed to maintain a positive
pressure on the borehole casing over a prolonged period of time without attention,
and to fix the sonde in place whilst avoiding transmitting any stresses.
Güralp Systems hole locks are constructed to order from accurate measurements of
your borehole at the depth you wish to install the instrument. Either single-jaw or
three-jaw hole lock units can be manufactured.
In installations with sand back-fill, or where the instrument rests on the bottom of
the borehole, a hole lock may be unnecessary.
2.3.1 The single-jaw hole lock
The single jaw hole lock is the standard option for triaxial borehole instruments. It
consists of an active clamp arm and a number of skids or studs on the sonde body.
The arm is attached to a compression spring, which forces it to swing out from the
sonde and wedge the body against the borehole wall. A textured steel jaw at the end
of the arm provides maximum grip against the borehole casing. The skids or studs
and the locking arm together form a multi-point clamp, which aligns the sonde body
parallel to the axis of the borehole and holds it firmly in place so that it cannot twist
or slip under the influence of ground vibrations.
There are several configurations of skids and studs which can provide a suitable
clamp. Either
8
Issue G - November 2019
