Vaisala PTB220 User Manual download pdf (Page 37)

CHAPTER 4_____________________________________________________________ COMMISSIONING

VAISALA _________________________________________________________________________ 31

x = pressure reading (in current unit)

This command is used to define the maximum pressure difference

between the pressure readings from different pressure transducers

(P1/P2 or P1/P2/P3). If the defined value is exceeded, the relevant

digits in the ERR field (see FORM command) will change from 0 to 1.

It is recommended to use the ERR field as part of the FORM

command definition, if there are two or three pressure transducers in a

PTB220 series digital barometer. More than one ´1´ in the ERR field

indicates that the pressure reading output of the barometer is not

reliable.

Following basic cases may occur for barometers with two or three

pressure transducers (only the differencies found between the readings

from the pressure transducers are important):

Two transducers: Three transducers:

P high

P low

Pdmax ?

P high

P low

P middle

Pdmax ?

For an acceptable measurement crucial conditions are:

- two transducers: P high - P low ≤ Pdmax

- three transducers:

P high - P middle ≤ Pdmax and P middle - P low ≤ Pdmax.

The factory setting for Pdmax is 1 hPa.

Example of setting the limit to 0.5 hPa:

>pdmax <cr>

Pd max : 1.000 ? 0.5 <cr>

Examples of exceeding the Pdmax limit in case of two and three

pressure transducers:

>form <cr>

4.2P""UUUU #r #n

?4.2P1""P2""P""UUU""ERR#r#n<cr>

>send <cr>

1020.30 1020.32 1020.31 hPa 00

>send <cr>

1020.30 1022.30 1021.30 hPa 11

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Vaisala PTB220 User Manual Page 37