SUMMARY: Temperature monitor

From: william.m.gilroy (
Date: Wed Jul 21 1993 - 22:55:57 CDT

What follows is a long summary of various temperature monitors. I
tried to trim most of the information, but I wanted to leave the
reader with a good impression of all of the products. There are
quite a few commercial products to handle this sort of problem.
Then some people sent me ideas on how to build a circuit to
do most everything that I want. I am going to take a two prong
approach to our problem. The first thing I will buy is a Gordon
Kapps model 125. This is designed to monitor PBX's and since we
will be getting a new PBX and the Kapps 125 is very well suited
for PBX monitoring and security. The second thing I will do
is build a circuit which will turn on an alarm, and kill the power
if a timer expires (~5 mins.) and it will either be triggered by the
Kapps unit, or a thermocouple, or both. I will have our electrician install
a device to kill the circuits that I need.
That way I am covered no matter what.
We also might purchase a Network Wizards WizTemp-2 to monitor the
room temperature over time. It seems like a neat device and the
price is right. If you have any questions feel free to send me some mail.

Bill Gilroy

Thanks to (Peter da Silva)
Paul Guthrie <> (Trammell B. Hudson)
ephsa!carrbc (Brian C. Carr) (Rennie Allen)
ANDREW BENSON <> (Steve Flaherty)
rrd@hpfcso.FC.HP.COM (Ray Depew) (Network Wizards) (Roy Pillay ,@hicam,x175) (Doug McCarthy ~)
Paul Leeson <>

-------------------- cut here ------------------------

After an A/C failure, we're in the process of programming our BEST
UPSses to shut off power on overtemp. With a little more work you
could monitor them from the serial port and do that under control
of your own systems. (make sure you sync() first!) Other UPS'es
also have this feature. Since I currently do not have a UPS this
won't work for me.


Network Wizards today introduced the WizTemp-2 RS-232 based temperature
sensor. This second generation sensor is ideal for machine-room and
environmental temperature monitor applications.

The new unit is packaged in an RS-232 connector shell, and includes a
temperature sensor with a 12' monitoring probe. Software, including source
code, is available for most Unix systems. The software includes a daemon
to monitor and record the temperature, and activate user-configurable
alarms when abnormal conditions are detected. Additional functions include
programs to print or display daily temperature graphs on terminals,
PostScript printers, and X windows. The price for one sensor starts at
$179. Contact Network Wizards at; phone (415) 326-2060;
fax (415) 326-4672.


Gordon Kapes Inc of Skokie Ill makes a model 125 site monitor.
It's really nice, a bit pricey, and is made to monitor PBX's remotely.
 It has the ability to monitor temp via an internal probe and an external probe. It also monitors about 8 relay contacts. Also it monitors 3 rs-232 ports both DTR level (equipment on/off) and data matching from the ports. It can dial out via a modem to external pager, voice mail, modem, whatever... It has the ability to do relay closures in response to any stimuli.

I have it set to monitor all alarms, temps, system failure rs232 messages, internal and external equipment temps... It has a nice real time display, you can dial into it, even has nice security features, (I know, I locked myself out and COULD NOT break into it) it would go into alarm if attempts ever are made.
So after 3 bad attempts I got a bunch of pages about intrusion alarms. You can tailor all criteria as you see fit. I went back and made it reasonable.

It is a really nice unit... I can't begin to tell you...
I even have it programmed to log into the vax and send me and a dist. list mail of all the alarms and a weekly status...

There is a peice of hardware which is called 'automatic operator'
for our UNIX system.
This small box is connected between the system and console.
It does nothing else than looking for system messages and other external
events and 'types in' commands to the system. It has a few connectors
shown below:

           - 2 event connectors for incoming signals (on/off switches)
           - 1 connector for uninterruptable power supply
           - 1 connector for main circuit breaker
           - 1 connector for speech synthesizer
           - 1 connector for modem (dial in/out)
           - 1 dial extension

It has 9 free programmable menus and is very easy to program (like basic).

e.g. if the temperature in out computer room raises upt to 35 degrees
the ATOP shuts down the system after 60 Seconds, calls the operator
via the automatic dialing extension and 'tells' him a specified text
with the speech synthesizer, or waits until the temperature is back to
normal and starts up the system again.

This does not quite fit my bill. I forgot to get the name of who manufactured
this product, but if you have to know send me mail.

Honeywell for one makes monitoring systems for machine rooms. The people that
supply your Halon system or a local fire alarm type company may also sell
such things. They are however expensive. I called Honeywell and got a
product brochure. There stuff is aimed at people who want to control
HVAC systems is large buildings with multiple zones.

The HOBO series of data acquisition tools from Onset Computer represent
another alternative for data acquisition using the HP48. They are small,
rugged, priced competitively (I didn't say "cheap").

I received a model of the HOBO-TEMP Miniature Temperature Logger, for a
30-day free evaluation. This is what I thought of it, after playing with it
for 30 days. Note that these comments may ramble a bit, and certainly don't
tell the whole story. I highly recommend that you contact Onset for more

The HOBO-TEMP is one of a whole family of miniature data acquisition products
from Onset Computer Corporation. For more information, you can contact them

Onset Computer Corporation
Pocasset, MA 02559-3450
Ph (508) 563-9000
FAX (508) 563-9477

For what it's worth, tell them I sent you.

They also have products available for:
Temperature (air, water, high T (>500 degC), medical, meat carcass, etc.)
Relative Humidity
Pressure (ambient, altitude, well hole, etc.)
Light Intensity
Salinity (conductivity)
Motion, vibration

and are working on units for:
Carbon Monoxide
Carbon Dioxide
Dissolved Oxygen

Out-of-the-box software is available for MS-DOS, MS-Windows, and Mac computers.
The bit-level communications are simple enough (and freely available) that
anyone could write the tools necessary to use a HOBO with their system. I
wrote some rudimentary tools for my HP48SX.

Initial Impressions
The entire module fits on a tiny SMT PC board, with components on both sides.
Components are sealed in encapsulant (except for the on-board battery and the
I/O connector). The assembly fits inside a 35mm film canister -- and that's
exactly what it is shipped in!

The I/O connector is a mini stereo headphone jack, identical to the ones used
on portable personal stereo equipment. The supplied interface cable connects
to the HOBO-TEMP on one end, and to a normal 9-pin serial port on the other

The HOBO-TEMP I got was shipped with the cable, extremely simple instructions,
and software for DOS and Windows. Software and DIN cable are also available
for the Mac.

The instructions are simple: You plug the HOBO-TEMP into your computer, start
the software, select the amount of time for which you wish to collect data,
then "Launch" it. Then -- get this -- you unplug it from the computer! The
HOBO-TEMP will conscientiously take and store up to 1800 measurements in the
time interval you requested, and then it will sit and wait for your return.
To retrieve the data, you plug it back in, start the software, and "Upload"
the data.

We have designed a system that does all you describe, and more. The system is
based on an industrial microcontroller, and supports any OS which supports
ordered shutdown from a UPS signal (i.e. we "or" the shutdown signal with the
UPS shutdown signal), although on UNIX platforms we can support much more
sophisticated interactions.
There are many other things I didn't cover, but if you are interested I'll
forward you additional information. The system isn't cheap >$2000.00 but it
is extremely flexible. It is designed to allow completely unmanned operation
of a computer system. One of the uses of the cabinet door cabinet monitor is
to log tape changes, in situations where you have some non-technical person
at a remote site changing tapes and you want to know when they forgot to do
it.... comes in handy...

This systems is overkill for my needs but it might fit someone else's. If
have the need for some custom work these people might be the ones to do
the job.

Quick summary:

Temperature monitoring:
        - High temp shutdown
        - Low temp shutdown
        - Multiple distributed thermocouples (allows averaging of room tem.
          to prevent false alarms, or to shutdown equipment in particular
          locations within the room, or building).
        - Tunable high an low values from the host OS (if UNIX )

Tamper monitoring:
        - Monitors computer cabinet doors through low cost microswitches
        - Up to 10 tamper inputs

Power control:
        - Controls up to 10 devices 120 or 240 volt
        - Positive control (i.e. command to stop, command to start, i.e. if
          the controller itself loses power, computers are not shut down).
        - Auto synchronization (i.e. when the controller is powered up it
          determines the current state of the system and synchronizes itself).

Monitoring features:

        - Max. temperature within configurable time limit
        - Min. temperature within configurable time limit
        - Avg. temperature within configurable time limit
        - Tamper switch on/off times.
        - Controller boot time
        - Power on time for each controlled device
        - Power off time for each controlled device

email: mail: Expert Technology Corporation

And now the stuff for people who like to tinker(i.e. Build your own).
I have left most of the information intact in case you want to try
this at home.

        A thermistor could be connected to an op amp configured as a comparator
with the output being buffered to the relay. Like this (pardon the ascii)

    |_| (Thermistor)
    | |
   +V | |\ (op amp)
    | +----| \______ to relay
    | +----| /
    | | |/

|> 2. If the temperature keeps rising talk to my computers to start a
|> software shutdown.
        That would be a little more difficult to build. As a possibility, a
dedicated terminal line could signal a daemon watching that port to initiate
a shutdown. Not to difficult, but it does require the system resources...

|> 3. After the software shutdown I will need some way of turning off
|> the power to the computers and other misc. equipment to bring
|> the room temperature under control.
        Same as with the light, only use a normally closed relay. Or, as an option,
use a timer calibrated to wait the length of time the shutdown takes. As a second
option, have the daemon be the last process killed and have it pulse the terminal
line to trigger the relay.

|> 4. Allow the temperature or unit to be monitored by a computer or remotely.

        Hmm, this would be more difficult. On the low end, I can see a tone
generator (basic oscillator) connected to the thermistor and the output to the
phone. A high freq. tone would be a signal to get in there RIGHT NOW, while a low
buzz would be the artic freeze signal.
        On the high end, an ohm meter (digital ladder type), connected to a
basic talking circuit to read the value from the meter and speak it over the phone.
This is rather impractical, but a possibility.


in an earlier incarnation i was an electronics engineer, to provide a warning
of future failures i designed a cheap and very simple/reliable monitor using
an industrial grade capillary temperature switch, a relay, a battery, a
really loud piezo-electric screamer and a push button switch

when it gets too hot the switch closes which enegizes the relay which
latches on (until you push the button and it is cool) and sounds the alarm

once a week we test it (turn the dial until it trips) once a year we change
the battery (it uses zero power until it trips)

this may seem a bit low-tech but if you look at plant control systems
they tend to use the same level of technology, because it is very reliable
and won't go wrong if you zap it with static or emi

if you use a spare relay contact to switch a line on a serial port you can
have a daemon running to detect it and start a shutdown or page you etc.

cutting the power means getting solenoid controlled contactors fitted
on the room power supply (in series and after the manual ones) these can be
fed from the battery/relay in the alarm itself

you can get neat looking cheap electronic thermometers with alarm outputs but i
wouldn't trust one to guard expensive systems, high-grade monitors tend to
have high-grade prices and come with extras like fire detection and control
for halon/CO2 flooding

if you want to monitor the temperature remotely get a thermocouple input
card and a relay card for one of the computers and then let it do the
monitoring/alarm sounding, National Instruments sell these (as do others)
use at least two thermocouple so it can spot failures

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