Vaisala HUMICAP HMP140A Guía de usuario descargar pdf (Pagina 25)

HMP140A SERIES

U175en-1.5 Appendix 3

1999-12-08 1

APPENDIX 3: HMP143A PROBE CABLE EXTENSION

The cable of the HMP143A probe can be extended up to 100 metres with the

help of the extension set including a junction box (part no. 19326) and a

shielded six wire extension cable (part no. 1535).

The junction box has a 5-pole terminal block and two PG9 lead-throughs. The

extension cable is a shielded 6 x 0.22 mm

copper wire cable. This cable

enables the extension without the need for transmitter adjustments. The user

can also use some other cable for this purpose provided that it is a shielded

copper wire cable. A shielded cable is recommended as it ensures the best

possible EMC protection. The diameter of the cable should not exceed 7 mm

as larger cables do not fit to the lead-through of the transmitter.

The HMP143A probe head uses a combined signal ground and supply voltage

ground. Ground wire resistance R

causes an offset type error to the

transmitter output. The error is -0.11 x R

both in %RH and in °C. This means

that if maximum error allowed is e.g. -0.3 %RH or -0.3 °C, the ground wire

resistance should not exceed 2.7Ω. The resistance of the cable 1535 is

minimized by connecting three wires as a ground conductor (see Figure 1).

Possible error can also be leveled out by readjusting the transmitter offset

(RH offset and T offset).

VIO

SHIELD

GRN (ground)

YEL

BRN

HMP143 PROBE

CONNECTOR

JUNCTION

CABLE SHIELD

VIO

SHIELD

GRN

YEL

BRN

PROBE CONNECTOR

BOX

EXTENSION

CABLE

BLU

GREY

YEL

BLK

HMP143 CABLE

THREE WIRES CONNECTED

TOGETHER (WHT, GRN, RED)

PROBE CONNECTOR ON THE

HMP143 PCB; THE COLOURS

SHOW THE DIRECT CONNECTION

OF THE HMP143 PROBE HEAD

Figure 1 Schematic of the extension set connections

1 2 ... 20 21 22 23 24 25 26 27 28

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