Remote Terminal Temperature Monitoring and Alarming
Build an interface to allow analog temperature readings and analog alarming thresholds to be set and viewable
on a remote terminal of all radio sites maintained by Jefferson County Sheriff's Office and partner agencies.
Design, build, test, and deloy a unit that will translate radio equipment room temperatures of extreemly remote
radio sites into analog values that interface to existing environmental monitoring equipment (SDM3000) which
can be displayed at a user terminal running Motorola's MOSCAD monitoring software. Additionally, add an adjustable
alarming setpoint that will trigger temperature alarms through the MOSCAD monitoring software.
Motivation for the project
As a radio maintenance technician maintaining radio sites composed of hundreds of thousands of dollars in equipment
each, I took great pride and interest in being pro active with the maintenance of the sites. Rather than wait for
equipment failures, it has always been my goal to put in place redundancies, conduct preventative maintenance, and
monitor the health of all equipment under my supervision.
When I was hired as a radio tech, I was introduced to the seven radio sites I would be maintaining, many of which we
have shared interest in with neighboring Counties and Statewide entities. Motorola's MOSCAD software suite is used
at a terminal in our central radio shop. It provides digital and analog I/O to each of the radio sites we maintain
by interfacing to rack mounted equipment known as the SDM3000.
Once I began to understand the system, its capabilities, and its limitations, I noticed two major issues:
-First, the previous technicians relied on commercial off-the-shelf thermostats located at the radio sites
to provide a digital alarm stating simply that there were temperature issues at the site. Their alarming
threshold began at 100 deg F.
-Second, analog monitoring at the MOSCAD remote terminal was not being used for anything at any of
the 200+ radio sites in the state of Colorado.
As technicians, we had no way of knowing what the real-time temperatures at a radio site might be. If the temperature in
the equipment room reached a high enough level (100deg F) to alarm us, equipment failure was already happening or imminent.
Some of our radio sites, especially in the winter, require hours of travel to access with a combination of conventional vehicles
and ATV's or Snowcats. We were forced to respond to environmental alarms with little context as to the severity of the situation.
We had the environmental system "backbone" already in place to provide the connectivity of digital and analog I/O between
the sites and a central control location. Why not leverage that technology to provide early warning of changes in environmental
conditions? Each site has its own personality based on geographical location, technologies used to manage temperature, and
historical stability of equipment. So, a variable alarming threshold would benefit the monitoring system.
I wanted to create a device that would provide the following functionality:
-Analog measurement of the room's temperature
-Translate the analog temperature reading to an analog value that could be interfaced to the SDM3000
which would then display the temperature on the analog software gauges at the central MOSCAD terminal
used for system monitoring at our radio shop.
-Calibration offset for the temperature to account for any drift or variation over time.
-Variable alarming threshold set by the user for each radio site.
-Visual feedback on the unit to display the current temperature, the alarming threshold temperature,
the current status if in an alarm condition and if exiting the alarm condition.
-If alarmed, the system would need to maintain that alarm status for a minimal amount of time to account
for latency in the connectivity over the closed network we maintain through various microwave
connections. Additionally, if the site's temperature is hovering right at the alarming temperature
temperature, we need to have a reasonable hysteresis in alarming.
-Digital alarm output to interface with to the SDM3000 and MOSCAD software which triggers email alerts.
There were two major constraints in building these devices was funding. As a local government agency, very little
money was available for the project. For that reason, I was forced to source all equipment and materials from
hobby level locations and local hardware stores. The second constraint was time. Due to the high paced work
environment and day to day responcibilities, I didn't have time to develope a product using a PIC microcontroller,
custom designed PCB's, and a more appropriate housing.
I developed the software algorithms to read the 0-3.3V analog temperature, process that value through a weighted
average algorithm, incorporate the calibration offset from an additional potentiometer, translate that value to a
temperature reading 0-100deg F, display that value on the LCD, and scale the 0-3.3V values to 0-5V values needed
at the inputs of the SDM3000 at the sites. The state machine was the conceptual backbone of the software to account
for the various states viewable to the user through the LCD. A menu button allows the user to see the current
temperature, the alarming setpoint temperature threshold, the status of alarming, as well as my contact information
should another agency have questions while troubleshooting the system.
Below are images of the resistive temperature device with enough cabling to allow it to reach reasonable locations
for temperature measurement and the final product as seen from inside. Again, these devices had to be produced
using materials around the shop or easily sourced locally. I would like to improve upon the design in the future
if time and funding allows.
The resulting devices have been deployed at six of our remote radio sites for about two years. They
have worked reliably with the exception of the LCD screens which would need to be reevaluated if
another iteration of design was to take place. They have become more dim over time from constant use.
The internal hardware still performs flawlessly and has
provided a lot of value to the monitoring of our equipment. Additionally, the devices have safeguarded
the radio equipment as we can now monitor the environmental conditions more closely. We can anticipate problems
before they happen which not only saves money in the replacement of equipment, but ensures we can keep
public safety radio systems on the air.
Below is an image of taken of how we now see the temperature displayed at the end user terminal through
the MOSCAD monitoring software (see gauge in lower left-hand corner). This particular site is extremely stable at just under 70deg F. For this
reason, I have set the alarming threshold at 75deg F. Although 75deg F is still within reasonable
range for operation of equipment, if the temperature in the room ever exceeded that alarming point we would need to immediately
respond. Some major cooling system would have to fail in order for that to happen. The room's temperature would
quickly reach levels that would cause equipment failure.