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Note that if the isometer is built into a Network Rail style cubicle arrangement, the RS485 connection are brought-out at the base of the cubicle through the terminal block positions 18 and 19 If connecting directly to the isometer. Connect straight to terminals B and A. |
4-20mA
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Analogue Interface
Use of the 4-20mA output is not recommended, but the interface could be employed to connect multiple bender isometer units to a single TX SA380TX by utilising spare analogue inputs.
Be aware that the insulation resistance reading will be prone to error due to the strange equiation unusual equation used by the 4-20mA signal converter:
R equation
This COMING SOON - THE EQUATION USED BY BENDER
The SA380TX supports quadratic scaling of input vectors, and as such the above equation has to be approximated on an SA380TX using the following quadratic equation:
TX equation
ERROR PLOT
The COMING SOON - THE EQUATION USED BY THE SA380TX
The equations has been formulated to provide a good fit below 150 k Ohm. The error plot is shown below:
COMING SOON - 4-20mA ERROR PLOT
This plot also assumes the RK170 4-20mA output device is correctly calibrated.
The detailed set-up of this the 4-20mA is described below
Digtial Volt-Free-Contact Interface
Where a fault repeater exists, up to 12 digital outputs may be provided to indicate which sub-feeder is experiencing the worst insulation resistance. These are wired as per standard digital inputs
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