Halimeter® CALIBRATION METHOD
[Applies to older units, WITHOUT automation features. Generally, those shipped prior to October, 2002.]
To achieve a proper calibration, two separate procedures are required. The first is a typical instrument calibration against a known gas concentration, while the second procedure compensates for the vagaries of differing sensor response times.
It is possible to make field adjustments by using only the second procedure, but accuracy may be compromised if both procedures are not used.
For complete information, please consult our service department.
This method assumes a warmed-up and stabilized unit, operated by a knowledgeable user.
CALIBRATION AGAINST KNOWN GAS STANDARD – DONE FIRST
Prepare a ppb (parts per billion) level H2S gas standard. At Interscan, we do this by volumetrically diluting a 10 ppm (parts per million) H2S/nitrogen gas blend down to 240 ppb, using zero air or nitrogen.
Alternatively, a permeation calibration system can be utilized to generate an approximate 250 ppb H2S standard.
The gas mixture, either undergoing dilution, or directly from the permeation tube calibrator, will be delivered to a 50 ml (milliliter) glass manifold, at a flow rate that must be greater than the Halimeter® pump flow rate of 500 ml/minute. This manifold is used to simulate a mouth, as well as acting as a dilution chamber. The mixture in the manifold is then directed to the Halimeter®.
- Adjust the ZERO control knob so that the panel meter displays “000.”
- Insert the Halimeter’s inlet tube into the manifold.
- The meter reading will start to increase.
- When the meter reading stops climbing, adjust the CAL (in some units SPAN) control, so that the meter displays the ppb concentration of the calibration gas mixture.
- Remove the inlet tube from the calibration manifold.
COMPENSATION FOR SENSOR RESPONSE TIME – DONE SECOND
Based on the flow rate of the Halimeter’s pump, there is approximately 6 to 10 seconds duration of usable sample in the mouth. Under classical ambient air sampling conditions, it takes 30 to 60 seconds for the sensor to achieve its full response. Thus, sensor response time can affect a breath reading.
A fast responding sensor will show a slightly higher breath reading than a slow responding sensor. To compensate for this, the Halimeter® should be tested using a human standard.
To qualify as a human standard, the individual must have a “clean” mouth, and not have any halitosis problem. Often, this person is the dentist or hygienist. A human standard reading should be between 80 and 110 ppb. Ideally, there should be at least two human standards in the dental office.
In addition, three readings should be taken on each human standard, and an average calculated.
By way of comparison, a normal, non-dental person who has a “clean” mouth and who does not have a halitosis problem, often measures higher (up to 160 ppb), and will not be as consistent.
A new sensor, with a fast response, should always provide breath readings within one of these ranges, depending on whose breath you are testing. As a sensor gets older, and has seen considerable use, its response gets a little slower and it may need some “help.”
Proceed as follows:
- If readings on the human standard fall below the target range, adjust the calibration control (CAL or SPAN) up slightly until the breath readings are within the target range. (80 to 110 ppb)
- If readings on the human standard are above the target range, try using a different human standard to ensure that the first person tested did not have bad breath. If all of your human standards have readings above the target range, adjust the CAL (or SPAN) control down until the breath readings are within the target range.