Carbon Monoxide
Accessory Head
Model: ACM3
OPERATOR’S MANUAL
Description
The model ACM3 carbon monoxide accessory
head enables most digital multimeters to measure
low levels of carbon monoxide in parts per million
(PPM). It is intended to measure levels of CO in still
ambient air. In many cases, it can help pinpoint
sources of CO.
It uses a catalytic chemical sensor that con-
sumes no chemicals. Life is primarily determined by
the type of exposure.
The most practical application is to determine if
the indoor CO levels are higher than outdoor levels
and to determine the source. This instrument
detects changes in CO levels very quickly.
"Walk around" test
The ACM3 is fast enough to respond almost
instaneously to changes in CO levels in the air. If
you see a difference in CO levels from outside to
inside, you need to find the source of the CO. Walk
around and watch the display. By constantly going
towards the area of highest concentration, you can
determine the source of the CO. It may be that
someone just drove their car into the garage and
opened the kitchen door and you don't have to take
any action. Or it could be that the furnace is starved
for air and that CO is entering the house. You've got
to fix that.
How to use
1. Connect to COM and Volts jacks using the
Fieldpiece deluxe test leads. For Fieldpiece
“stick” meter, slide the head directly over the
meter.
2. Select the 2000mVDC range.
3. Turn on. Let stabilize 45 seconds.
4. Take the instrument outside and adjust it to
zero. Then bring inside to take measurements.
5. Expose sensor to a still, stable air sample (see
precautions). The display reacts to the presence
of CO in seconds. Take final reading when
reading stabilizes.
6. For initial tests, walk around the building, watch-
ing for the readings to go up to determine where
maximum concentrations of CO are. To meas-
ure air from register, use a pump or measure
out of the air stream. Hot blowing air can
adversely affect the reading. The temperature of
the sample must be near ambient.
Zero adjust
As needed, adjust reading to zero in a known
zero CO atmosphere and in temperature similar to
the sample air to be tested and when ambient air is
within specifications and head is in equilibrium
(temperature and relative humidity) with ambient.
Specifications
Range:
0 to 1000PPM (2000PPM with 5 minute
max exposure time.)
Initial accuracy:
0-15ppm ±5% reading ±1 ppm after zeroing
15-35ppm ±5% reading ±2 ppm after zeroing
0-1000ppm ±5% reading ±5ppm after zeroing
Accuracy:
Stated accuracy at 73ºF±9ºF, <90%
relative humidity
Response time:
<70sec to 90% of reading
Operating temperature:
32 to 105 ºF
Operating relative humidity:
15 to 90%RH, non-
condensing
Storage temperature:
-4ºF to 140ºF, 0 to 80%
R.H. with battery removed from meter.
Long term drift:
<5% / year (depending on use)
Sensor calibration:
Factory calibrated on
205ppm
Sensor type:
Electrochemical (specific to CO)
Battery life:
200 hours typical. No measurable
current draw when in "off" position.
Battery:
9V
Average switch
The average switch averages the readings over
the last two or three seconds. This allows the user
to read more stable measurements.
CO detectors and cracked heat
exchangers
A CO detector cannot tell you if a heat exchang-
er is good. A CO detector can indicate a heat
exchanger maybe be cracked only if all of the fol-
lowing conditions occur simultaneously:
1. The flame generates high concentrations of CO
(lack of oxygen, excess fuel, high temp).
2. Enough exhaust gases are emitted from the
heat exchanger crack.
3. The exhaust gases from the crack are not dilut-
ed too much before coming in contact with the
sensor. A cracked heat exchanger may leak CO
in a small stream. You may measure high con-
centrations at one point but low concentrations
only an inch away.
4. The heat exchanger is the only possible source
for the CO detected.
Precautions
1. Do not measure gas engine exhaust or other
high CO or highly contaminated gases. High
levels of CO and other contaminants can ruin
the sensor.
2. Do not take readings directly in stream of air at
register or in a flue.
3. Allow enough time for accessory head to reach
ambient temperature and RH%.
Air being measured must be stable and between
32ºF and 105ºF and 15%RH and 90 %RH.
Temperature and humidity changes can cause tran-
sient readings. For best results, use a AOXP2 pump
to sample the air, cool it to near room temperature,
and raise the relative humidity.
CO exposure effects
Effects can vary significantly depending on
age, sex, weight, and overall health.
Coffee cup test
To demonstrate that your CO head works, turn a
ceramic coffee cup upside down and slide it over
the edge of a counter (or desk) to expose about a
third of the mouth of the cup. Burn a cigarette
lighter inside the exposed mouth of the cup. Don't
burn the counter. When the flame starts to flicker,
you've burned up most of the oxygen in the cup cre-
ating carbon dioxide and now you're starting to pro-
duce CO (carbon monoxide). Bring the flame in and
out of the mouth of the coffee cup to just keep the
flame alive. The longer you keep the flame flicker-
ing, the more CO you produce. After 10 seconds of
flickering, extinguish the flame and put the CO head
in the mouth of the cup. You should see readings in
the 100s. Take it out if it approaches 1000PPM.
CO ppm
Effects
9 ppm
Minimal. Max allowable concentration
for eight hours (EPA and ASHRAE).
35 ppm
Max for continuous exposure for one
hour (EPA and ASHRAE).
50 ppm
Max for eight hours (OSHA).
100 ppm
Trips installed CO detectors. UL2034
specifies a max exposure of 100 min.
200 ppm
In two to three hours: slight
headache, tiredness, dizziness,
nausea. UL2034 specifies a max
exposure of 35 min.
400 ppm
In one or two hours: frontal
headaches. In three hours: life
threatening. UL2034 specifies a max
exposure of 15 minutes.
800 ppm
In forty five minutes: dizziness,
nausea, and convulsions.
800 ppm
In two to three hours: death.
1600 ppm In one hour: death.
6400 ppm In fifteen minutes: death.
12800 ppm In three minutes: death.
WARNING
Do not take measurements directly at a
tailpipe, in a furnace flue, or at a register. See
precautions.
Do not rely solely on a carbon monoxide
measurement to determine if a heat exchanger
is bad. See paragraph on left.
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