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Close on Alarm
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Monitoring circuit
(close on alarm)
Relays wired
in parallel
OPTIONAL 4-20 MA INTERFACE
The TTDM-128 can be equipped with an analog 4-20 mA interface which can
communicate the status of a selected SIM channel. The TTDM-128 adjusts its current
output based on whether an alarm condition exists in the selected channel, and (when a
leak is detected) on the location of the leak.
The module’s output can be scaled to make full use of the 4-20 mA range for the length of
sensing cable connected to the selected SIM channel. <HOW??>
IMPORTANT: The 4-20 mA interface communicates the status of a single SIM channel. The
default SIM channel is the TTDM-128 internal Sensor Interface board. To use the port for
a different SIM channel, select 4-20 mA SIM from the 4-20 mA Test menu (as described at
the end of this section).
NOTE: The current output is isolated from the sensing circuit and therefore requires an
external DC power supply (26.4 V maximum). The maximum loop resistance (Rmax) is
determined according to the power supply voltage:
Vdc Rmax
24 900 ohms
18 600 ohms
12 300 ohms
4-20 mA Wiring
Before wiring the external equipment to the TTDM, check that jumpers J11 and J12
“OPTION PCB INT PWR JMPRS” on the TTDM Mother Board are not installed.
The 4-20 mA output port is connector J2 on the TTDM-128 motherboard. The external
power supply and monitoring device can be connected as per either of the following
diagrams:
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