Fig. 8.3(b)
Fig. 8.3(c)
8.3.1 Step 1:
(One time only.) To merge the high-power portions of the transfer curves, we apply
a temperature-dependent translation at the output amplifier. This is effected by RT3, RT4 and S2
in Fig. 2(c). To calibrate this translation for the chosen output slope, one proceeds to make a look-
up table as follows:
For example, assume you are going to use a 12k (tempco = 0.007/
0
C) sensistor. Choose RT4 =
51k, RT3 = (51-12)k = 39k, and put in a pot in place of S2. For a temperature rise of 60
0
C, S2 will
increase to 18.2k. Measure the output with the pot set at 12k and 18.2k. The actual shift induced
over 60
0
C will be slightly (about 10%) more than the difference you measure here. Repeat the
measurements changing RT4 and RT3 in order to come up with a look-up table which can be used
for all units with this output slope setting.
8.3.2
Step Two:
Run the transfer curves for the unit at -55
0
C and +85
0
C (or whatever
extreme temperature values you require). The measured curves should not be displaced by more
than approximately 1.5 dB from the room-temperature curve; if they are, check the regulators to
see if they are within spec. From the table developed as described in section 8.3.1, chose
appropriate values of RT4 and RT3 to merge the high-power portion of the transfer curves
measured at +85
0
C and -55
0
C with the room-temperature transfer curve.
8.3.3
Step Three:
Look at the observed output values at the start of logging for each
temperature. Adjust these observed values for the calculated effect of the temperature-dependent
translation needed to merge the high-power portions of the transfer curves, as estimated in Step 2,
above. For example, suppose that the procedure of Step 2 resulted in predicted shifts of +3/4 dB
and -3/4 dB at 85
0
C and -55
0
C, respectively. To allow for this effect, you would subtract 3/4 dB
from the -55
0
C value, and add 3/4 dB to the +85
0
C value. The observed high- and low-
temperature output values at the start of logging, after this correction, should be displaced from
the room- temperature value about equally (within about one dB), but in opposite directions.
Neither value should deviate from the room- temperature value by more than about 5 dB,
depending on how low the start of logging has been set.
-28-
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