Installation, operating and maintenance manual
UNIGAS 300
DDG6004MHGB/08-2017/Rev.A2 Software version from M 1.3.40 and D 2.3.37
8
T: conversion with C=pfix/pb x (tb + 273.15)/(t + 273.15) x 1(Z-Zbfix)
TZ: conversion with C=pfix/pb x (tb + 273.15)/(t + 273.15) x Zb/Z
PT: conversion with C=p/pb x (tb + 273.15)/(t + 273.15) x 1/(Z/Zbfix)
PTZ: conversion with C=p/pb x (tb + 273.15)/(t + 273.15) x Zbfix/Z
where pfix, tfix and Z/Zbfix are fixed, preset values.
If an error condition occurs for pressure or temperature, or in determining the compressibility, or in the event
of a CRC error in the firmware for the conversion functions, conversion will be continued as described below,
with replacement values pfix, tfix or Z/Zbfix being used for pressure, temperature, Z or Zb.
The error condition is indicated by a blinking exclamation mark (!) in the display (display in main screen 1, see
chapter 6).
In the error condition:
•
counting continues in Vm1 and Vc1
•
conversion in Vb is stopped
•
the relevant status bit is set (see chapter 6):
o
pressure measurement fails or is outside range of pmin to pmax:
alarm pressure
and
error p
or
t
o
temperature measurement fails or is outside range of tmin to tmax:
alarm t
and
error p
or
t
o
determination of Z fails:
error Z
or
Zb
o
Zb determination fails:
error Z or Zb
and
error Zb
o
CRC error in software responsible for conversion:
CRC error conversion
•
counting will continue in Vc1err
•
conversion takes place in Vb1err with relevant replacement values
o
pressure measurement fails or is outside range of pmin to pmax: t and pfix
o
temperature measurement fails or is outside range of tmin to tmax: p and tfix
o
determination of Z fails: p, t and Z/Zbfix
o
Zb determination fails: p, t and Z/Zbfix
o
CRC error in software responsible for conversion: p, t and Z/Zb
•
the display shows the values of pfix, tfix or Z/Zbfix for p, t and Z/Zb.
The responses to an error condition as described above, apply to an instrument with conversion on the basis
of PTZ. For the other versions, T, TZ, PT, conversion for p, t or Z and Zb takes place with tfix, pfix and Zbfix,
so the response to failure of p, t, Z or Zb does not apply.
The compressibility Z and Zb are calculated according to an algorithm. The following algorithms are available
for UNIGAS 300:
•
AGA NX19 modified (Gasunie)
•
SGERG TM5 1991 method 1-4
•
AGA 8 gross method 1
The algorithm stored in UNIGAS 300 (see main label), is a complete algorithm. This means that interpolation
or tables are not applied. Consequently, the accuracy of the calculation of Z or Zb will match the accuracy of
the algorithm itself.
Specific gas compositions are known for which - at certain temperatures - the compressibility cannot be
calculated correctly by the algorithm. UNIGAS 300 itself will detect such a case and handle it as a failing Z or
Zb calculation and continue the conversion as described above.
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