Test Setup of Thermocouple Simulation
Figure 329
Inspection
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Typical Thermocouple Installation
Figure 330
Inspection
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Uncompensated Cold Junction
Thermocouple Simulation
Figure 331
Inspection
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(5) In previous example the desired input voltage (temperature) was known and the unwanted junction voltage was subtracted from the desired input in order to obtain the correct voltage for the thermocouple voltage source. In the following example, Equation 2, the voltage of the thermocouple voltage source is known, such as when a temperature switch point is being checked, and the temperature associated with it is to be determined. In Equation 1 the desired input is Equation 2’s “unknown input”.
Equation 1
.
Existing Input
.. . . . . .
.. . . . . .
.. . . . . .
.. . . . . .
Desired
.. . . .
.
..... .
Input from
Thermocouple
Voltage Input
Temp
.
from
=
Unwanted
.
Equation 2
.
.
Voltage Junction Source
.
.
.
.
Existing Input
.. . . . . .
.. . . . . .
.. . . . . .
.. . . . . .
Unknown
.. . . .
.. . . .
Input from
ThermocoupleInput from
+
=
Temp Unwanted Voltage
..
.
(6) Most electronic control temperature tolerances are on the order of ±20 to ±40F. The temperature simulation circuit should be 10 times more accurate than the allowable tolerances for the electronic control. This means that the temperature simulation circuit
.
should be accurate to within ±2 to ±4F. This includes the errors in measurement of the room temperature for the cold junction voltage.
(7) Referring to an alumel-chromel thermocouple table, note that the millivolt reading for 1000F is 22.251 mv and for 1001F is 22.274 mv. The difference for this 1F Delta is 0.023 millivolts or 23 microvolts. This indicates that the voltmeter used for the thermocouple simulation voltage should have an accuracy and resolution of 0.01 millivolts or 10 microvolts. With such an accurate voltmeter, more error (1-1/2 to 3-1/2F) is allowed for the room temperature reading errors. Note that a 4F error in measuring the room temperature means a 4F error in calibrating the control.
Voltage Junction Source
.
.
.
.
Inspection
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N. Composite Material Components
(1) Check per Table 308.
Table 308. Inspection/Check Criteria and Repair Limits for Composite Material Components.
MATERIAL COMPOSITION OR ITEM/TYPE OF DAMAGE USABLE LIMITS MAXIMUM REPAIR LIMITS
LAMINATE
Delamination None permitted. All must be repaired. Maximum repair limits: 25% of component total area.
Cuts, Scratches, Blemishes Any that does not expose fiber reinforcement. All cuts that penetrate fiber reinforcement, or are visible or require further processing are repairable.
Cracks None permitted. Surface resin crack that does not penetrate fiber reinforcement. Cracks in reinforcement are not acceptable.
Frayed Surface None permitted. All must be repaired. Maximum repair limits: 25% of component total area.
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