Power and cable recommendations - WMT700

WMT700 Series User Guide

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User guide
This applies to hybrid cables (CBL210706-2M, CBL210706-10M, CBL210706-15M, CBL210706-26M, CBL210706-SPEC).
The hybrid cable ambient temperature can be up to 60 °C (140 °F). Cable installation is limited to up to 3 cables in contact with each other horizontally (on tray) or vertically (on wall).
  • For the fully heated WMT700, if you need a hybrid cable longer than 26 m, Vaisala recommends ordering a special length cable (CBL210706-SPEC).

    To extend the cable length, you can also use the connector, your own cable, or the 2 m hybrid cable (CBL210706-2M), a junction box, and your own cable.

    To wire WMT700 with your own cable and a connector, the minimum requirements are
    • 2 parallel 1 mm2 wires for the heating power supply
    • 2 parallel 1 mm2 for return (ground) because of high current need
  • The operating power supply must be at least 0.25 mm2 for supply and return (ground).

    The temperature specification for the cable is 80 °C (176 °F). This allows the cable ambient temperature to be up to 60 °C (140 °F).

  • For the other versions (non-heated, transducer-heated, and transducer-and-arms-heated), the installation ambient temperatures are lower.

    For your own cable, the maximum temperature is higher than 80 °C (176 °F). Refer to the cable standard DIN VDE 0298-4, or equivalent standard, to define the correct number of parallel wires and cross section areas for the 13 A circuit breaker for heating power supply and for the 1 A circuit breaker for operating power supply.

The minimum operation voltage for a fully heated WMT700 (heated transducers, arms, and body) is 16 V, including the cable losses, if a separate power supply unit is used for operation.
Connect both heating power supply wires to the same ferrule if the cable is shortened.
The following figures illustrate the wiring of heated WMT700 instruments.

The following figures illustrate the wiring of heated WMT700 instruments.

Figure 1. Wiring of heated WMT700 versions
When you use separate power supplies for operating and heating, the minus (-) terminals of the power supplies are connected together by an additional wire. Use a minimum 0.75 mm2 wire for connecting the (-) terminals together.
CAUTION There are 2 terminals connected in parallel for both positive and negative rails of the heating voltage for the maximum current capacity. If the connection cable has parallel supply wires, they all must be connected to ensure current capacity. Leaving one terminal unconnected or connecting it to the ground may cause a WMT700 malfunction or a short circuit in the power supply.
Always use cables that meet the minimum dimension requirements.

Long cables with thin wires cause power loss in the cable and significantly decrease WMT700 heating capabilities. Loop resistance of 0.15 Ω results in an approximately 1 V drop in heating voltage with 200 W heating. The loop resistance of a 10-m cable (CBL210706-10M) is 0.2 Ω resulting in an approximately 1.3 V drop. Vaisala recommends using at least a 28 V supply for the maximum heating capability.

Table 1. Power supply requirements with hybrid cable
Hybrid cable length Hybrid cable (CBL210706-2M) with 2 x 1 mm2 for supply

2 x 1 mm2 for return current

2 m hybrid cable (CBL210706-2M) with 2 x 1 mm2 for supply

2 x 1 mm2 for return current extension with 2.5 mm2 cable

2 m hybrid cable (CBL210706-2M) with 2 x 1 mm2 for supply

2 x 1 mm2 for return current and extension with 4 mm2 cable

2 m 24 V DC 400 W 24 V DC 400 W 24 V DC 400 W
10 m 24 V DC 400 W 24 V DC 400 W 24 V DC 400 W
15 m 26 V DC 400 W 26 V DC 400 W 24 V DC 400 W
26 m 28 V DC 400 W 27 V DC 400 W 24 V DC 400 W
30 m 29 V DC 400 W 28 V DC 400 W 24 V DC 400 W
40 m 31 V DC 400 W 30 V DC 400 W 24 V DC 400 W
50 m 33 V DC 400 W 32 V DC 400 W 25 V DC 400 W
60 m 35 V DC 400 W 33 V DC 400 W 25 V DC 400 W
70 m - 35 V DC 400 W 26 V DC 400 W
80 m - - 26 V DC 400 W
90 m - - 27 V DC 400 W
100 m - - 27 V DC 400 W