NSM-3E Signal Monitor Unit
Operations Manual
Eberle Design Inc.
Page 3
Section 2
Extended Features
The following extended features are provided on the NSM-3E Signal Monitor for additional
monitoring functions, and to increase the reliability of the NSM-3E Signal Monitor operation.
2.1 HARDWARE FEATURES
The NSM-3E Signal Monitor is a microprocessor based unit. All monitoring functions and
features are firmware programmable which permits upgrades or modifications by simply
reprogramming the flash memory containing the firmware with the upgraded version. Thus,
most changes to the NSM-3ESignal Monitor 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
microprocessor based RMS-Engine controls the analog to digital (A/D) hardware which
samples each AC input voltage a minimum of 32 times per cycle. The RMS-Engine then
calculates the true RMS voltage value producing accurate results which are virtually
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 is utilized to retain fault status information in the event of an AC
Line power interruption. The correct fault indications will be displayed upon restoration of
AC Line power. This EEPROM nonvolatile memory requires no battery back-up. No
monitor configuration programming is stored under battery power.
2.2 DUAL INDICATION MONITORING
This monitoring function detects simultaneous indications of active Green, Yellow, Walk,
and Red field signal outputs on the same channel on the NSM-3E Signal Monitor. A Dual
Indication fault places the NSM-3E Signal Monitor into the fault mode causing the Output
relay contacts to transfer. Dual Indication Monitoring is enabled concurrently with
Clearance Monitoring on a per channel basis via the front panel SSM switches.
Dual Indication Monitoring is disabled when the Red Enable input is not active.
NOTE: An open or no load condition (i.e., open field wire) may be detected as an active
signal depending on the output impedance characteristics of the load switch, and may
cause a Dual Indication fault.
2.2.1 GY-DUAL INDICATION MONITORING
This monitoring function detects a simultaneous indication of active Green and Yellow field
signal outputs on the same channel. It can be used to monitor channels which have an
unused Red field signal output tied to AC+ (i.e. five section signal head) and is enabled by
placing the front panel option switch labeled "GY ENABLE" in the ON position. A GY-Dual
Indication fault places the NSM-3E Signal Monitor into the fault mode causing the Output
relay contacts to transfer. GY-Dual Indication Monitoring may be enabled concurrently with
Dual Indication Monitoring. When GY-Dual Indication Monitoring is enabled, ALL channels
which have NOT been selected for Dual Indication Monitoring via the front panel SSM
switches will be individually monitored for simultaneous indications of active Green and
