COSA Xentaur Xentaur HDT - Manual (Page 36)

Appendices
page 29
vide a useful output. Consider an example where the area of
interest to be monitored is 10 to 100 ppmV, and the analog
output is set up with the factory defaults of -100°C to +20°C
(which is 0.014 to 23612 ppmV); then the current loop out-
put will vary only from ~4.1 to ~4.2 mA in the area of inter-
est (consult with the graph on the following page). In most
instances this would be an unacceptable output for proper
monitoring of the measurement. In this example the user
should adjust the analog output low & high ranges such that
the output range is better suited to the measurement of 10 to
100 ppmV. It may be useful to select the low and high
ranges to be 5 and 150 ppmV respectively, thus out of range
conditions will be detected properly. Then the low range
will be set to 5ppmV which is -65.5°C dewpoint, and the
high range will be set to 150ppmV which is -38.5°C dew-
point. Now the current loop output will be 4.55 to 14.48 mA
in the range of 10 to 100 ppmV, the ~10mA variation is
more than sufficient for a good measurement by the user’s
equipment. One may carry out similar calculations for LBS
or G/M3 and choose the appropriate settings. While making
these computations it may be useful to obtain a copy of
Xentaur’s dewpoint calculator, this is a Microsoft Win-
dows™ program which simplifies the process of converting
dewpoint measurement units. It is available at www.xen-
taur.com. If you are not certain how to carry out such calcu-
lations send, by e-mail to [email protected] or by fax to
(516) 345-5349, your system specifics, and some one will
get back to you with appropriate analog output settings.
In general, if the dewpoint is monitored in °C or °F, there is
no need to change the factory default -100°C to +20°C set-
tings, because the 4-20mA provides sufficient resolution to
measure the output better than the specified accuracy of the
sensor.