The maximum allowable field wiring resistance between the transmitter and the IOTA connection terminal is dependent upon the voltage requirement of the transmitter. The formula for calculating the maximum wiring resistance for the Series C UIO channel used as an analog input is given by the following equation.
The Digital Input module requires the installation of a bleed resistor (approx. 22k ohm) at the
switching device between the 24VDC source and the terminal providing the switched signal. If this
resistor is not installed and open wire detection is enabled (OWDENBL = ON) a false open wire
alarm will be generated whenever the input device is not closed (i.e., PVRAW = OFF).
If open wire detection is enabled (OWDENBL = ON) and the IOM detects the broken-wire condition,
then
l PVCALC will be NaN, in which case, PVAUTO will be NaN.
l Soft Failure 179 'Open Wire Detected' is generated, and
l PVRAW and PVAUTO will consequently be set to OFF.
Note that Open Wire Detection is supported only with the 24VDC IOTAs and not for the following:
l The high voltage DI modules
l The DI-SOE module
l The GI-IS IOTAs
If a GI-IS IOTA (CC-GDILxx) is used, open wire detection as described above may not be used.
l In these cases, OWDENBL must be set to OFF for all channels.
l As an alternative to Series C open wire detection, you may use the Line Fault Detection (LFD)
feature of the MTL Switch/Proximity Detector Interfaces.
MTL Switch/Proximity Detector Interface is the third party equipment from MTL which enables
safe-area loads to be controlled by switch or proximity detectors located in a hazardous area.
Two replay output are provided. Independent phase reversal control allows an alarm condition
to be signaled for either state of the sensor. A selectable line fault detects (LFD) facility detects
an open or short circuit in either field circuit. It is not part of any agency certification or CE
certification.
o If LFD is enabled (through a switch on the device) for any channel, two resistors must
be installed: a 22k ohm resistor across the switch and a 680-ohm resistor in series
with the power supply lead. This feature detects both open and short circuits. When
LFD is enabled and a line fault is detected the MTL device illuminates an LED
indicator and forces the channel data to OFF.
o If a MTL4510, MTL4511, or MTL4516 device is used, there is no indication to Experion
PKS.
o If the MTL4517 is used channel 31 is energized to ON. Note that for the MTL4517 if
any channel has LFD enabled channel 31 is not available for use as a general
purpose input - for the other three devices channel 31 is always available.
