901-0014 Rev A
Calibration
3.0 Introduction
All analyzers are factory calibrated prior to shipment.
There is no easy answer as to how often zeroing and calibration should be
performed. This is strictly a function of the application. Sensor zeroing
compensates for signal drift and sensor calibration compensates for any possible
decrease in sensitivity of the sensor. The primary cause of sensitivity
decrease is excessive loss of water in the sensor by evaporation. This is due to
time and temperature, or prolonged exposure to a high concentration of gas.
The instrument is best calibrated by introducing a known concentration of gas and
adjusting the span control to the proper ppm level. The calibration gas must be
accurate. The sources of gas standards include commercially available gas
mixtures diluted with air or nitrogen in cylinders or permeation devices.
3.1 Interscan’s Sensor Express®- Electronic
Calibration Service
Interscan’s Sensor Express® program streamlines downtime by sending you pre-
calibrated sensors on a regular basis per your needs, without the burden of returning
sensors to our factory for re-certification. The sensors are shipped to you either
two(2), three(3), or four(4) times per year based upon factory recommendation.
Follow the instruction received with the sensor, allow stabilization, and the
instrument is ready for use. The factory recommended procedure for calibrating all
Interscan analyzers, involves certified calibration gas or a permeation device
system. Besides being essential for calibration, having a known certified gas
standard on hand allows the user to test the analyzer at any time to determine that
it is fully operational.
As indicated on the certification sheet, the Sensor Express® does not certify the
analyzer as a whole. Most importantly, the Sensor Express® program is not a
substitute for basic analyzer maintenance, nor does it check for malfunction of the
analyzer components.
3.2 Sample bag Calibration & Pressurized Cylinder
Calibration
Whatever the source of calibration gas, the recommended method is to collect the
gas in the proper sample bag, which is then attached to the analyzer INLET. The
calibration gas is drawn from the proper sample bag through the sensor. An
exception to the use of a sample bag is for those gases, which are reactive with, or
chemisorbed by the bag itself (e.g. Chlorine, Hydrazine). Teflon® or Tedlar® bags
are suitable for H2S, SO2, NO and NO2. Several bag materials are suitable for CO.
A 5-liter bag is recommended.
