Section 3
Installation
19
FT702LT Flat Front Wind Sensor Manual
3.3.3
Surge protection
All connections from the wind sensor to any computer equipment and power supply should run through Surge
Protection Devices (SPDs). This will suppress any unwanted overvoltage transients present on the signal or
power lines. The surge suppression devices are to be UL 1449 listed.
The ratings of the SPDs must be suitable for the surge conditions. Assuming that appropriate shielding and
termination has been used throughout, then the SPDs used with our sensor should have a minimum surge
current rating of 20kA (8/20µs) and be capable of clamping the output below the maximum input voltage
accepted by the electronic systems they are connected to. This will prevent any surges or large voltage
differences being present at the inputs to the wind sensor, data acquisition electronics or power supply.
The SPDs should be installed as close as possible to the point where the signals enter the cabinet in order to
prevent noise propagating to other electronics. The SPDs should also be grounded appropriately. Figure 14
shows how the SPDs should be installed.
Figure 14: FT702LT digital interface surge protection
The supply pair [24VDC / 0VDC] is electrically isolated from the other lines and the chassis. The triple RS-485
signal wires [Data ground, Data A, Data B] are isolated from the other lines and the chassis. The data ground
can be directly connected to the chassis of the data acquisition cabinet.
Some examples of SPDs suitable for this protection are given in Figure 15 below from manufactures, DEHN &
Söhne GmbH. (
Manufacturer
Type
Manufacturers part number
PSU lines
Phoenix Contact Module (x1)
PT 2PE/S 24 AC
RS485 lines
Dehn
Module (x1) - BCT MOD BE 5 & BCT BAS
919 620 & 919 506
Phoenix Contact Module (x1)
PT 3-HF-12 DC
Figure 15: Typical SPD configuration used to protect sensor
Figure 16 shows an example of how the wires are
up the SPD’s inside a Phoenix Contact control cabinet. The
termination of the cable shield at the wall of the control cabinet using a cable gland is not shown.
