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PICOLINK -
An Optical Fibre Link Between the AVS-47B and AVS47-IB
PICOLINK offers a solution to customers having problems with ground currents or high-frequency interference in their resistance thermometry systems. It is a low-speed fibre optic link connecting the AVS47-IB Interface to the AVS-47B Resistance Bridge. The PICOLINK option is installed in the factory into a new bridge and a new interface which are purchased together. The optical link becomes an alternative to the standard Picobus cable. If the original Picobus is needed -e.g. for connecting the AVS-47B directly to a PC- then the PICOLINK can be easily disabled.
Optical fibre links that are available for RS232 communications cannot be used with the synchronous Picobus protocol. The reason is that we require four fibres instead of only one or two. Therefore we based the PICOLINK design on four low-cost 1-millimeter plastic fibres. These fibres are placed in a common tube, which is heat shrinked to form a cable of about 6-8 mm in outer diameter. The length of the standard cable is 5 meters.
The PICOLINK further consists of two receiver/transmitter circuit boards, which are mounted on the inner sides of the AVS47-IB and AVS-47B rear panels. The emitters and receivers do not require connectors: the fibre ends are just pushed into them and tightened. The fibres can be cut using sharp end cutters, if the ends must be renewed for some reason. In addition to lower price, one advantage of a connectorless cable is that it can be pulled more easily through the wall of the shielded room.
PICOLINK provides the best solution in a case where the Picobus cable is suspected to act as an antenna. Such a situation can arise, for example, when the AVS47-IB box is located outside the shielded room but the shield of the Picobus cable cannot be grounded to the conducting wall for some reason. Picolink provides galvanic isolation without voltage limits. It is not, however, the only way to cut ground currents - also the standard wire-Picobus provides optical isolation inside the AVS-47B.
PICOLINK is completely transparent in use.
PICOLINK uses visible red light, which makes it easier to verify its operation.