Most programmable logic controllers (PLCs) contain a timer that runs continually when the PLC is in the RUN mode. What is the function of this timer?
What will be an ideal response?
The function of this timer is to prevent the computer from becoming hung in some type of loop. If the timer is not reset at the end of each scan, the watchdog timer will reach zero and all outputs will be turned off.
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The consolidation of concrete on a construction site are generally done
A) using a power-driven rod vibrator. B) using a power-driven plate vibrator. C) manually using a 1-in.-diameter, 3-ft-long steel rod. D) manually using a 2-in.-diameter, 3-ft-long steel rod.
Oxygen is never used to purge an HVAC system because _____.
a. oxygen will contaminate the system b. an explosion could occur under certain conditions c. oxygen contains too much moisture d. oxygen is too expensive to use for that purpose
Which method enables ultraviolet (UV) lamps to be able to kill the maximum number of microbes in a duct system?
a. Install UV lamps in the airstream ahead of an EAC. b. Constantly bathe the evaporator coil with UV light. c. Cycle the UV lamps on and off with the furnace blower. d. Install UV lamps in the return air duct airstream.
Define field use
What will be an ideal response?