4-1
Section 4
CALIBRATION AND MAINTENANCE
4.1 GENERAL
The Model 3900 low humidity generation system requires little periodic maintenance.
Following the proper operating procedures as given in this manual will help assure trouble-
free operation of this system.
4.2 CALIBRATION
Proper calibration of the temperature and pressure transducers is critical to the accuracy of
the generated humidity. Each time a transducer is calibrated its current calibration
coefficients and calibration date are stored to non-volatile memory.
Calibration of the system requires the following support equipment:
1) Temperature:
A. Temperature bath with a liquid medium (recommend Fluorinert FC-77, a 3M
product), a range of 0-50 °C, and stability of ±0.01 °C or better. Less stable baths
may require the use of a thermal block.
B. Standard or reference thermometer (PRT or Thermistor) for the range of -80 to 10 °C
for the saturator temperature, and 0 to 50 °C for the test temperature both having a
resolution of 0.01 °C or better. Thermometer accuracy should be ±0.03 °C or better.
2) Low Pressure Range:
A. Static gas pressure source for the pressure range of ambient to 50 psi, 3.5 bar, or 3500
hPa absolute with a stability of ±0.0025 psi, 0.00017 bar, 0.17 hPa or better.
B. Standard or reference pressure gauge for the range of ambient to 50 psi, 3.5 bar, or
3500 hPa absolute with a resolution of ±0.0025 psi, 0.00017 bar, 0.17 hPa or better.
Reference pressure accuracy should be ±0.025 psi, 0.0017 bar, 1.7 hPa or better.
3) High Pressure Range:
A. Static gas pressure source for the pressure range of ambient to 300 psi, 21 bar, or
21000 hPa absolute with a stability of ±0.01 psi, 0.00069 bar, 0.69 hPa or better.
B. Standard or reference pressure gauge for the range of ambient to 300 psi, 21 bar, or
21000 hPa absolute with a resolution of ±0.01 psi, 0.00069 bar, 0.69 hPa or better.
Reference pressure accuracy should be ±0.10 psi, 0.0069 bar, 6.9 hPa or better.
4) Flow:
A. Standard or reference flow meter for the range of 0 to 5 standard liters per minute
with a resolution of 0.01 L/min or better. Flow meter accuracy should be ±0.05 L/min
or better.
