Matco Tools MD79 Manual Del Usuario página 12

2) When using Capacitance function, discharge capacitor(s) before
making any measurements. Large value capacitors should be
discharged through an appropriate resistance load
DCA Current function
Inputs are made through the test lead terminals COM/+.
Application notes:
The DCA function is designed especially for HVAC/R flame sensor
applications. The 0.1A resolution is useful for identifying the minute
current changes in flame detector applications. Flame signal current
check should indicate steady flame signal of at least 2A for a
rectification type, or 1.5A for an ultraviolet type (8A for self checking
systems). If a flame signal current with inadequate strength or
fluctuation beyond 10%, check the following to avoid the risk of
unwanted flame relay dropout :
For gas or oil flames (Minipeeper):
• Low supply voltage
• Detector location
• Defective detector wiring
• Dirty viewing windows
• Faulty Minipeeper
For oil flames (Photocell):
• Detector location & wiring
• Smoky flame or poorly adjusted air shutter
• Faulty Photocell
• Temperature over 165
For gas flames (Flame Rod):
• Ignition interference (A flame signal current difference with the
ignition both on and off greater than 0.5A indicates the presence
of ignition interference)
• Insufficient ground (must be at least 4 times the detector area)
• Flame lifting off burner head (ground), or not continuously in
contact with the flame rod
•
Temperature in excess of 600
insulator causing short to ground.
o o
F (74 C) at photocell
o
F (316
o
C) at the flame electrode
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