Welch Allyn SureTemp PlusModule - User Manual - Manual (Page 70)

Calculating the Bias SureTemp Plus Module OEM Implementation
70 Confidential Welch Allyn OEM Technologies
4. After the two temperatures are collected, perform the same procedure over a few different
temperatures (such as 75F, 85F, 95F, 105F) to verify that the temperature deltas are linear. If
the deltas are not linear, the design team must review the implementation of the SureTemp
Plus module. Design venting into the host product to allow for temperature equalization.
Calculating the Bias
Calculate the bias value as:
Probe ambient in well (
°
K) minus Probe ambient out of well (
°
K).
The differential number can then be converted to IEEE floating point, and then converted into the
corresponding 4 bytes needed for the (943A) Set Ambient Bias Command. For example:
Probe Well ambient temperature = 26C (299.1
°
K)
Room ambient temperature = 24C (297.1
°
K)
Difference = 2
°
K
Saving Ambient Bias
Either of the following approaches to applying the programmable ambient bias is acceptable.
• Implement a factory procedure where the host's ATE sets this value once via the 943A
command and then follows with the 2A06 command to write the bias value to the
module’s EEPROM.
• During each power-up and initialization of the host device, the host sends 943A to set the
module’s ambient bias in RAM (rather than saving it to EEPROM).
Module Factory Default: The SureTemp Plus module defaults the ambient bias value to 0.56 K.
Effect of an incorrect ambient bias: For every 1 degree C the device reads the ambient too high,
the predict result will be lower by 0.045.
note The previous ambient temp is held by the SureTemp Plus module for 3 minutes. At the
end of the 3 minutes, the module gets a new ambient temp from the first probe reading
prior to heating the tip. This means that the probe must be in the well without interruption
for 3 minutes to collect a new ambient temp.
Data 00 00 00 40 (= 2.0 IEEE float)
Host sends 03 02 10 94 3A 01 04 00 00 00 00 40 D8