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7
Theory of Operation
The Armstrong ST6700 AIM
®
transmitter is designed to continuously monitor any type of steam trap. It utilizes
a combination of hardware and integrated algorithms to accurately detect steam trap conditions. The hardware
consists of an acoustic sensor (Piezo) and a temperature sensor (Thermistor). The integrated algorithms are
patented, proprietary code designed by Armstrong to provide actual steam trap conditions based on inputs from
the hardware. When applied to a steam trap, the device wirelessly transmits the current condition of the steam
trap.
The ST6700 has built-in algorithms, which perform a series of diagnostic checks in order to determine the
condition of the steam trap.
The rst stage validates the surface temperature of the steam line and compares it with the congurable
temperature set point. The temperature sensor located in the stem of the monitor detects the skin temperature at
the inlet of the steam trap. The Stem Temperature is compared to the Temperature Set Point.
If Stem Temperature is less than the Temperature Set Point, then the steam trap is cold/plugged. This could be
due to a failed plugged steam trap, or there is no steam distributed to the steam trap. If the steam trap is cold/
plugged, the transmitter will return a Trap Condition value 2. A Trap Condition of “2” means the steam trap is in a
cold/plugged condition.
If the Stem Temperature is greater than the Temperature Set Point, the monitor assumes there is steam being
distributed to the trap causing the device to go into the second stage of diagnostics.
In the second stage, the ST6700 listens to the operation of the trap to determine if there is steam loss through
the steam trap’s internal orice. The Piezo sensor has been tuned to detect a trap passing live steam while
ltering out background noise. This acoustic signature is analyzed by Armstrong’s patented algorithm to
determine if the steam trap is in a blow-thru condition (i.e. - losing live steam).
If the algorithm determines that the trap is in normal operation, then the ST6700 will publish a Trap Condition
value of 1. A Trap Condition value of “1” means the trap is in a good condition.
If the algorithm determines that the trap is losing live steam, the ST6700 will publish a Trap Condition value of 3.
A Trap Condition value of “3” means the trap is in a blow-thru condition.
Armstrong ST6700 Measurements
Honeywell Yokogawa Nivis/Nexcom
Trap Condition Channel_9 Piezo Status Channel_9
Stem Temperature Channel_10 Temperature Channel_10
Temperature Set Point Channel_11 Temperature Setpoint Channel_11
Trap Condition Definition
1 OK Steam Trap
2 Cold/Plugged Steam Trap
3 Blow Through Steam Trap
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