5
maintain accurate rea ings the sensor calibration shoul be checke at least annually.
For sensors locate in areas where there is severe ust an atmospheric pollutants, it
is recommen e that the sensor be checke more often.
4.2 Fiel Checking Relative Humi ity
If the sensor to be checke is locate in a remote area, NovaLynx recommen s taking
along a secon RH sensor element to replace the original sensor element in case it is
out of the specific accuracy range. Due to the stability of the sensor esign, it is not
necessary to perform an actual calibration a justment to the sensor electronics.
Replacement of the sensing element is recommen e every two years for best results.
If a secon RH sensor is unavailable, the next easiest way to check the probe operation
in the fiel is to compare the relative humi ity sensor output against an accurate
psychrometer. If the humi ity rea ings are within ± 4% RH the sensor is goo an oes
not nee to be replace . If the rea ing error is greater, then the ecision must be ma e
whether to replace the sensor or to use it for a longer perio of time. Remember to
inclu e the accuracy of the test instrument (psychrometer) in the ecision process.
Most often the accuracy of the test instrument or psychrometer will be less than the
accuracy of the electronic sensor.
For best test results, the Assmann style psychrometer, NovaLynx Mo el 225-5230, is
recommen e . The Assmann psychrometer uses a spring- riven fan an has precision
thermometers. An easier metho is to check the sensor operation using a secon
electronic sensor such as Mo el 225-HM34-C. The 225-HM34-C uses the same
sensing elements an allows quick an easy checking of the humi ity an temperature.
Rea ing of the 225-HM34-C is irect using the built-in LCD isplay.
Shoul the RH probe appear to be out of calibration even after changing the sensing
element, contact NovaLynx for instructions. For best results, the RH sensor shoul be
teste in an accurate RH calibration chamber (such as the Mo el 220-HMK11) un er
controlle con itions.
Any signal con itioning provi e for use with the sensor has been a juste at the
factory by simulating the sensor with a precision DC voltage source. Verify that the
signal con itioning or monitoring equipment is operating correctly an make any
necessary a justments before testing the sensor. Retest the sensor with the signal
con itioning or monitoring equipment after making any a justments to etermine
whether or not the sensor is correctly calibrate .
NovaLynx offers the Mo el 220-HMK11 for checking the calibration of electronic RH
sensors by the user. The calibration chamber uses saturate salt solutions to check the
%RH at 75% an at 12%. The calibration chamber works best in stable temperature
con itions such as those foun in oors or in laboratories, but can also be use to make
quick an accurate fiel tests of an electronic humi ity sensor calibration since the
chamber is always at the in icate humi ity. Sensor rea ings can be taken within 5
minutes. The chamber humi ity rea ing is correcte accor ing to the temperature
