Welch Allyn SureTemp PlusModule - User Manual - Manual (Page 69)

SureTemp Plus Module OEM Implementation Programmable Ambient Bias
Welch Allyn OEM Technologies Confidential 69
10 - Programmable Ambient Bias
Introduction
Predictive thermometry requires knowing the temperature of the probe tip at the start of a
measurement. To reduce the potential for fluctuations in tip temperature from one environment to
the next as the probe is removed from the well, the host must make sure the probe-tip
temperature in the well is as close as possible to room ambient. This can be a difficult task.
However, the module provides flexibility by means of a programmable ambient bias.
The programmable ambient bias is a compensation to account for temperature differences
between the probe-tip environment (when in the well) and the ambient room temperature.
The bias value is dependant on the given host system’s thermal rise and does not change for any
particular module/probe. Therefore, once a bias value is determined for a given host system, that
value can be used in subsequent SureTemp Plus modules intended for that configuration of host
system.
Determining the bias value would typically be a development team function, involving
temperature testing of the finished device over a range of temperatures to verify linearity. The
following provides an example of the procedure.
Host Device Temperature Testing
It is critical that the OEM developer uses a "normal" use model for this test. For example, if it is
normal for the finished device to run on batteries and the device when charging is warmer, they
should use the non-charging value.
Air movement around the device must be minimized. Keep the unit away from fans and drafts to
enable the unit to reach operating temperature.
1. A dummy temperature probe (not electrically plugged into the device) is inserted into the
probe well to control the switch. An active (plugged-in) probe is outside of the well, soaking in
room ambient for at least 5 minutes. The active probe tip must not be not touching any
surface; it must be free and clear and acclimated to room ambient. When operating
temperature has stabilized, the host pulls the dummy probe from the well and reads ambient
temp data from the temp packet. This number is recorded as the room ambient temperature
for later use.
2. The same active probe used to determine ambient temperature above is now placed into the
well of the finished device and allowed to soak for at least 5 minutes in the device/probe well
ambient.
3. The active probe is pulled from the well, and the host collects the ambient temp from the
temp packet. This number is recorded as the probe well ambient temperature for later use.