Inspection
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L. Pressure Drop Check: Cleaned Metallic Filter Elements Check pressure drop of cleaned filter element as follows: NOTE: Check pressure drop of a new filter element to establish baseline data for use during checking of cleaned filter elements.
(1)
Install filter element in test setup similar to that shown in Figure 328.

(2)  
Adjust regulator (1) to apply an inlet air pressure of 20 psig (137,89 kPa) as indicated on inlet pressure gage (2).

(3)  
Pressure indicated on downstream pressure gage (4) should not exceed pressure measured for a new filter element.

(4)
Replace filter element if pressure is excessive.

3.  RESTRICTOR UNIT (0.042 INCH (10,66 MM) DIAMETER ORIFICE)
2.  INLET PRESSURE GAGE 4. DOWNSTREAM PRESSURE (0 TO 30 PSIG) GAGE (0 TO 30 PSIG) (O TO 206,8 KPA) (O TO 206,8 KPA)
Test Setup of Filter Elements
Figure 328

Inspection
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M.  Thermocouple Simulators for Calibration and Checkout of Electronic Equipment
(1)  
For test purposes in simulating a thermocouple, a common and recommended method is shown in Figure 329 and Figure 331. Note that the voltmeter must be connected to the copper leads of the voltage source and not to the alumel and chromel input wires to the electronic control. The thermocouple junctions created by the thermocouple voltage source connections to the alumel-chromel wire are compensated by means of the ice bath. This is because the alumel-chromel thermocouple tables are based on an unwanted junction (reference junction or cold junction) at 32F (0C) the temperature of melting ice. The input leads to the electronic control are alumel and chromel wire, therefore, there are no thermocouple junctions, due to dissimilar metals, at the interface to the electronic control. A comparison of this thermocouple simulation to a typical thermocouple temperature measurement installation is shown in Figure 330.

(2)  
Temperature simulation without using an ice bath or other compensation is used but must be well understood in order to avoid unwanted errors.  The temperature of the unwanted junction, which is room temperature, must be measured accurately, and then used to correct the simulated input voltage.

(3)  
Using Figure 329 as an acceptable setup where the unwanted copper-alumel and chromel-copper junctions are at ambient temperature, then any voltage input from the thermocouple voltage source must be corrected for this existing ambient temperature input.  Note that an ice bath was used for the junction temperature in the previous example.

(4)  
For example, suppose the input required is 1200F (648,8C), and the room temperature is 77F (25C). To determine what voltage would be required from the thermocouple voltage source in Figure 329, refer to an alumel-chromel thermocouple table. The voltage for 77F (25C) is 1.000 millivolt, and 1200F (648,8C) is 26.975 millivolts.  Since the circuit of this figure, with zero thermocouple source voltage, is inputting 1.000 millivolt (ambient of 77F (25C)), then the input required to simulate 1200F (648,8C) (26.975 millivolts) is:

Existing
Input
from Input
..
..
. . . . .... . . . ...
. . . . ...
.
Desired Input
from
Thermocouple Voltage
.. ....
. ...
26 975mv
.
 1.000mv  25.975mv
=
1200F
Unwanted
Junction

Source
. . . . ...
Inspection
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