SSM-LE Series
Operations Manual
Eberle Design Inc. Page 7
Section 3
Enhanced Features
The following enhanced features are provided on the Eberle Design SSM-LE Series for
additional monitoring functions and to increase the reliability of the SSM-LE Series monitor
operation.
3.1 HARDWARE FEATURES
The SSM-LE Series is a dual microprocessor based unit. All monitoring functions and
features are firmware programmable which permits upgrades or modifications by simply
reprogramming the Flash memory device containing the firmware with the upgraded
version. Thus, most changes to the SSM-LE Series specifications may be accommodated
without modifying the hardware.
Since all critical timing functions are accomplished by the microprocessor, the quartz
crystal based accuracy results in very precise and repeatable measurements. This
accuracy is maintained on functions from timing fault conditions to implementing a unique
firmware based digital sampling and filtering algorithm. This algorithm is applied to all AC
field signals to help eliminate false detection in a "noisy" AC line environment.
Input voltages are measured using a true Root Mean Squared (RMS) technique. A
dedicated microcontroller RMS-Engine controls the analog to digital (A/D) hardware that
samples each AC input voltage at least 32 times per cycle. The RMS-Engine then
calculates the true RMS voltage value, producing accurate results which are very
insensitive to changes in frequency, phase, wave shape, and distortion. Voltage references
are temperature compensated for constant voltage levels within the operating temperature
range.
A nonvolatile EEPROM device is utilized to retain fault status information and event logs
through an AC Line power interruption. The correct fault indications will be displayed upon
restoration of AC Line power. This EEPROM device requires no battery back-up. The time
of day in the SSM-LE Series is stored in a battery-backed real time clock circuit. Should this
battery fail, only current time of day and date information will be lost. No monitor
configuration programming is stored under battery power.
3.2 DUAL INDICATION MONITORING
This monitoring function detects simultaneous input combinations of active Green and
Yellow, Green and Red, Yellow and Red, Walk and Yellow, or Walk and Red field signal
inputs on the same channel. When voltages on any two inputs of a channel are sensed as
active for more than the Dual Indication Fault time (7.4), the SSM-LE Series will enter the
fault mode, transfer the OUTPUT relay contacts to the Fault position, and display the DUAL
INDICATION status screen. The SSM-LE Series will remain in the fault mode until the unit
is reset by the RESET button or the EXTERNAL RESET input. When voltages on any two
inputs of a channel are sensed as active for less than the Dual Indication Fault time, the
SSM-LE Series will not transfer the OUTPUT relay contacts to the Fault position.
Dual Indication Monitoring may anticipate and prevent a possible conflicting signal display
in the intersection in the event that a proceed signal on the current phase hangs up and is
constantly detected as active. An open or no load condition (i.e., burned-out bulb) may be
also detected as an active signal depending on the output impedance characteristics of the
load switch (i.e. load switch leakage current), and may cause a Dual Indication Fault.
Dual Indication Monitoring will be disabled when the RED ENABLE input is not active. A set
of switches labeled “SSM” is provided on the SSM-LE series Signal Monitor front panel to
enable Dual Indication Monitoring on a per channel basis. See Section 5.3 for the
programming procedure.
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