Sherborne Sensors Keeps ZED Tunnel Guidance On Target

April 2011 Vol. 66 No. 4

ZED Tunnel Guidance, located in London, U.K., specializes in development and manufacture of advanced guidance systems for Tunnel Boring Machines (TBMs).

With an expected operational life of more than five years, if properly maintained and serviced between projects, Zed’s tunnel guidance systems rely on the engineered aspects of precision, reliability and robustness. Sherborne Sensors’ 2-axis servo inclinometers allow TBM operators to accurately identify the pitch and roll of the TBM relative to gravity, and ensure that the specified designed tunnel alignment (DTA) is delivered. This ensures a highly accurate tunnel is driven, with increased speed and at lower cost.

Calibration is achieved via precision analogue circuitry and analogue to digital converter.

“With the design that we had, it was not easy calibrating the inclinometer correctly in conjunction with the electronics PCB,” recalls Mick Lowe, senior project engineer at Zed Tunnel Guidance. “The cost in terms of labor was high, so we wanted an inclinometer with a narrower range of scale factors that would allow us to calibrate all of our PCBs the same way, and enable any PCB to work with any inclinometer, rather than having to pair each individually for each target unit produced.”

Space at a premium
In its simplest configuration, Zed Tunnel Guidance systems employ a combined target unit that is mounted at a convenient location on the TBM and incorporates both optical (laser) and gravitational sensors (servo inclinometer); a processor display unit (PDU) functioning as the main display and computer for the TBM operator; a junction box controlling the exchange of data between the target unit and the PDU; and a small set of tools and test equipment. In order to establish the present position of the TBM, the PDU requires information from the target unit, the DTA (design tunnel alignment) table and the user. The DTA table plots the course the TBM must follow, and can include up to 20,000 reference points. During installation of the guidance system, measurements are entered manually into the PDU by the user, informing it of the position of the target unit relative to the axis of the TBM.