Altitude adjustment – Welch Allyn TM286 Auto Tymp - User Manual User Manual
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Routine Maintenance
Welch Allyn TM286 Auto Tymp
gradient (GR) Using the same sequence, place the probe in the test cavity opening
labelled 2.0 cm
3
. The resulting tympanogram should be identical other than the ECV
should read 2.0 cm
3
. The same sequence can be followed with the 5.0cm
3
opening on
the test cavity. To keep a record of this test cavity calibration check, simply press
the
button on the front panel of the instrument.
Since sound pressure will vary with altitude and barometric pressure, some variation from
the 0.5, 2.0 and 5.0 cm
3
readings may be observed. The instrument is carefully calibrated
at our factory, which is at approximately 850 feet above sea level. An elevation of 1000
feet or higher, the instrument may need to be recalibrated to account for elevation (See
below for more details). It is not necessary to recalibrate for
barometric pressure changes on a daily basis. Keep in mind that a change in barometric
pressure (i.e., from low to high or vice-versa) will slightly affect the test cavity readings. To
keep a record of this test cavity calibration check, press the Print All
button on the
front panel of the instrument.
Altitude adjustment
The altitude calibration adjustment enables a "correction" to the ear canal volume (ECV)
measurement and test cavity volume measurement for variations due to altitude. The
instrument is a pressure sensitive device that makes measurements relative to ambient
air pressure. Changes in air pressure due to weather or altitude will affect the ECV
readout of the instrument. The slight pressure change resulting from changing weather
conditions will usually yield volume readouts with ±0.1 cm
3
of the expected cavity value,
but pressure changes due to altitude can shift these cavity values by as much as 30%.
These changes in pressure do not affect the accuracy of the compliance measurement
system in any way. However, it will affect the ECV values. The altitude calibration mode
allows adjustment of the Auto Tymp without the services of a qualified Welch Allyn
representative.
Table 1. 226 Hz Altitude Correction
226 Hz Probe
Altitude in Feet
Equivalent 2.0 cc Reading
0
2.0 ±0.1
1000
2.1 ±0.1
2000
2.2 ±0.1
3000
2.2 ±0.1
4000
2.3 ±0.1
5000
2.4 ±0.1
6000
2.5 ±0.1
7000
2.6 ±0.1
8000
2.7 ±0.1
9000
2.8 ±0.1
10000
2.9 ±0.1
Note
Operation of the system at an altitude of 10,000 feet may affect the ability to
pressurize to the maximum 5.00 cm
3
.