Tenma ST-8920 User manual

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User Manual
Part Number: ST-8920
Pressure & Flow Meter

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Table of Contents
1. Features.................................................................................................................... 3
2. Specications .......................................................................................................... 3
3. Button ....................................................................................................................... 4
4. Display Elements..................................................................................................... 5
5. Changing Setup Options......................................................................................... 6
5-1. Setup Options...........................................................................................................................................6
5-2. Entering or Exiting Setup ........................................................................................................................6
5-3. Changing a Setup Option ........................................................................................................................6
5-4. Duct dimension units Setting .................................................................................................................6
5-5. Duct Shape and Parameters Setting ......................................................................................................7
5-6. Choose Duct Shape .................................................................................................................................7
5-7. Parameters Setting ..................................................................................................................................7
5-8. Auto Power Off Mode...............................................................................................................................8
5-9. Menu Setting.............................................................................................................................................8
5-10. Ciear Memory Setting ............................................................................................................................9
5-11. Measuring Pressure ...............................................................................................................................9
5-12. Measuring Velocity...............................................................................................................................10
5-13. Measuring Flow ....................................................................................................................................10
5-14. Displaying Temperature ......................................................................................................................11
5-15. Holding the Displayed Readings ........................................................................................................11
5-16. Viewing the MIN, MAX, and AVG Readings........................................................................................11
5-17. Saving Samples....................................................................................................................................11
5-18. Recall and Clearing Sample Data .......................................................................................................11
5-19. Error Codes ..........................................................................................................................................12
5-20. Replacing the Batteries .......................................................................................................................12

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1. Features
• Larger LCD display with backlight.
• Relative time clock on MAX, MIN and AVG provides a time reference for measurement.
• Pressure, velocity or air ow measurement provides Zero Adjust.
• Display pressure, Air velocity or air ow plus environment Temperature simultaneously.
• Easy to calculate the area of a rectangular or circular duct.
• USB interface, USB to UART Bridge Controller.
• Low battery indication, and Auto Power Off mode (Sleep mode) increases.
2. Specications
2-1. General Specications
2-2. Manometer specication
1 psi*27.68=inH20
1 psi*68.947=mbar
1 psi*703.072= 1*mmH20
1 psi*6894.6=Pa
FSO: Full Scale Output
Operating Conditions 0°C to 50°C
Storage Conditions -10°C to 60°C
Power Supply 1×9V Battery
Low Battery Indicator Yes
Dimensions 203mm×75mm×50mm
Relative Humidity Non condensing (<10°C) 90% RH
(10°C to 30°C)75% RH (30°C to 40°C) 45% RH
(40°C to 50°C)(Without Condensation)
Accuracy ±0.3% FSO(25°C)
Repeatability ±0.2% (Max.±0.5% FSO)
Linearity/Hysteresis ±0.29% FSO
Pressure Range 5000 Pa
Maximum Pressure 10psi
Response Time 0.5 Seconds typical
Over range Indicator Err.1
Under range Indicator Err.2
Units Range Resolution
PSI 0.7252 0.0001
mbar 50 0.01
inH20 20.07 0.01
mmH20 509.8 0.1
Pa 5000 1

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2-3. Range of Air Velocity
2-4. Rang of Air Flow
CFM(ft3/min) =Air Velocity(ft/min)×Area(ft2)
CMM(m3/min)=Air Velocity(m/s)×Area(m2)×60
CFM: cubic feet per minute
CMM: cubic meters per minute
2-5. Range of Temperature
3. Button
1. Press to turn the thermometer on or off.
2. Press “MAN/MIX” to step through the maximum, minimum, and average readings. To exit the MAN/MIX/AVG mode,
press the “MAN/MIX” button for 2 seconds to return to normal operation.
3. Press “P/V/F” to show the air velocity, press “P/V/F” secondly to show the high and length of a rectangular or the
diameter circular duct, press “P/V/F” thirdly to show the air ow, press “P/V/F” to show differential pressure again.
4. Press “Hold/Zero” to freeze or unfreeze the displayed readings. Press “Hold/Zero” button and hold 2 seconds to
zero out the display.
5. Press “Save/Clear” button to store sample data. Or press “Save/Clear” button to clear sample data in Recall mode.
6. Press “Setup ” button to turn on the backlight. Press it again to turn off the backlight. Press “Setup ” button for
3 seconds to start or exit Setup. (See “Changing Setup Options.”)
7. Press “Unit ” to changes the temperature units. In Setup mode, press “Unit ” to scroll to the Setup option you want
to change or press “Unit ” to increase the displayed setting. In Recall mode, press “Unit ” to select the desired
sample number.
8. Press “Unit ” to Changes secondly showing number units. In Setup mode, press “Unit ” to scroll to the Setup
option you want to change or press “Unit ” to increase the displayed setting. In Recall mode, press “Unit ” to select
the desired sample number.
9. Press “Avg/Rec” button and hold 2 seconds to enter Recall mode. In Recall mode, press “Avg/Rec” to calculate the
sample data. In Setup mode, press “Avg/Rec” button to enter a Setup option. Press “Avg/Rec” again to store the
displayed setting in memory.
Range Resolution Accuracy
°C 0°C to 50°C 0.1 ±1°C
°F 32°F to 122°F 0.1 ±2°F
Air Flow Range Resolution
CFM 0-99.999ft3/min 0.0001 to 100
CMM 0-99.999m3/min 0.001 to 100
Air Velocity Range Resolution Accuracy
m/s(meter per second) 1-80 0.01 ±2.5% of reading
at 10 m/s
ft/min(feet per minute) 200-15733 1
Accuracy is function
0.1 of velocity and
duct 0.01 size
km/h(kilometers per hour) 3.6-288 0.1
MPH(miles per hour) 2.24-178.66 0.01
Knots(nautical miles per hour) 2-154.6 0.1

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4. Display Elements
1. min: sec or hour: min Display..
2. Pressure, Velocity, Flow or temperature modes are active
3. Primary Display.
4. Units of air velocity.
5. Units of pressure.
6. The indication of meter communicating to PC.
7. Auto Power Off mode indicators.
8. Duct Shape choices.
9. Low battery indicator. Replace the battery as soon as the low battery indicator appears.
10. Data Hold indicator.
11. The units of H, W or D.
12. Entering or exiting setup mode.
13. Indicates that a stored sample (or all samples) is about to be deleted from memory.
14. The sample memory is being accessed and the number of samples.
15. Annunciators showing that sample memory is being accessed.
16. REC, MAX, MIN and AVG indicators.
17. Temperature units of primary display.
18. Units of air ow.
19. Temperature units of secondly display.
20. Digits for temperature and time.

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5. Changing Setup Options
Use Setup to chose duct shape and set the duct parameters. Sleep mode, Max/min/avg mode menu setting and clear
memory. The thermometer stores the settings in its memory.
5-1. Setup Options
5-2. Entering or Exiting Setup
When the thermometer is in Setup mode, the display shows SETUP.
Press “Setup ” button for 2 seconds start or exit Setup.
5-3. Changing a Setup Option
• Press “Unit ” or “Unit ” to scroll to the setup option you want to change.
• Press “Avg/Rec” to indicate that you want to change this setting.
• Press “Unit ” or “Unit ” until the setting you want to use appears on the display.
• Press “Avg/Rec” to store the new setting in memory.
Notes: Setup is disabled in MIN/MAX/AVG mode.
5-4. Duct dimension units Setting
• When the meter is in Setup mode, Press “Unit ” or “Unit ” to scroll to the duct
• Dimension units setup option.
• Press “Avg/Rec” button. It shows “in” or “em” on the display.
• Press “Unit ” or “Unit ” to scroll to the setup option you want to change.
• Press “Avg/Rec” to store the new setting in memory.
Option Menu item Settings
Duct dimension units
Duct Shape and parameters
Unit
Duct Shape
Set duct dimension units in or cm
Set area of measuring air ow
Auto Power Off mode SLP auto off or on
Menu setting ENU 1, 2,or 3
Clear Memory Mem clear Yes or No

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5-5. Duct Shape and Parameters Setting
When the meter is in parameters setup mode. The screen is show number of the last duct shape and size that is entered. If
the duct is different than the stored version, then nd the proper duct type for the measurement (rectangular or round).
5-6. Choose Duct Shape
• When the meter is in setup mode, Press “Unit ” or “Unit ” to scroll to the duct shape setup option.
• Press “Avg/Rec” button. The screen shows the “ ”(rectangle) or “ ”(circular).
• Press “Unit ” or “Unit ” to scroll to the setup option you want to change.
• Press “Avg/Rec” to store the new setting in memory and enter parameters setup option.
5-7. Parameters Setting
• If duct is rectangle, the height of duct numbers and “H=” will be rst shown in the primary show.
• Press “Unit ” or “Unit ” button to select the decimal point.
• Press “save/Clear” to change the station of ashing digit and press “Unit ” or to “Unit ” change the ashing digit
from 0 to 9.
• Pres “Avg/Rec” button, the width of duct numbers and “W=” will be shown in the primary show.
• Press “P/V/F” button to select the next digit.
• Press “Save/Clear” to change the station of ashing digit and press “Unit ” or to “Unit ” change the ashing digit
from 0 to 9.
• Press “Avg/Rec” to store the new parameters in memory.
• If duct is circular, the diameter of duct numbers and “D=” will be shown in the primary show then select the duct diameter
that you want to use in the same way.

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5-8. Auto Power Off Mode
The meter enters sleep mode (default). That is to say, the meter will automatically shut off after 20 minutes if no button press
occurs for 20 minutes. When the meter is in Setup mode, the display shows SETUP.
Press “Unit ” or “Unit ” 11 to scroll to the “SLP” page . Press “Avg/Rec” to indicate “On” or “OFF”. Press “Unit ” or
“Unit ” until the setting you want to use appears on the display. Press “Avg/Rec’’ to store the new setting in memory. On
(sleep mode on) or OFF (sleep mode off).
5-9. Menu Setting
• When the meter is in Setup mode, Press “Unit ” or “Unit ” to scroll to the
• Mode Menu setup option.
• Press “Unit ” or “Unit ” to scroll to the setup option you want to change.
• There are three choices for selecting.
“1”. Display pressure and air velocity value.
“2”. Display air velocity and air ow value.
“3”. Display pressure, air velocity and air ow value.
• Press “Avg/Rec” to store the new setting in memory.

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5-10. Clear Memory Setting
• When the meter is in Setup mode, Press “Unit ” or “Unit ” to scroll to the clear memory setup option.
• Press “Save/Clear’’ to select the desired sample. There are three choices for selecting.
PRESS VEL FLOW: clear all pressure, velocity and ow sample data.
PRESS: clear all pressure sample data.
VEL: clear all velocity sample data.
FLOW: clear all ow sample data.
• Press “Unit ” or “Unit ” until the display show ‘’YES”, Press “Avg/Rec”, then clear the memory.
5-11. Measuring Pressure
The Primary Display number is Pressure
value, the device measures Gauge/Differential
Pressure 5000Pa, it features 5 selectable units
of measure: PSI, mbar, Pa, in H20, mmH20.
• Press “P/V/F” to enter the pressure mode
and press “Unit ” to select unit.
• Connect a single hose to the “Input (+)” port,
leaving the “Ref(-)” port unconnected.
• With the tubing open to ambient conditions
press and hold “Hold/Zero” for 2 seconds to
zero out the display.
• Place the input hose in a different zone than
the Meter.
• The Meter displays the differential pressure of
the input zone with respect to the reference
zone. For instance, a positive reading means
that the input zone is positively pressured
with respect to the Meter location or its
reference zone.

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5-12. Measuring Velocity
The Meter uses standard ambient conditions (temperature=21.1°C/70°F, barometric pressure= 14.7 PSI / 1013 mbar), to
approximate actual velocity and ow. The primary display number is air velocity, the device measures air velocity, and it
features 5 selectable units of velocity measure: m/s, ft/min, km/h, MPH, knots.
• Press “P/V/F” to enter Velocity mode and press “Unit ” to select unit.
• Connect the hoses to the pitot tube and to the Meter. The “Input(+)” pressure port on the Meter connects to the white hose
from the total pressure connection of the pitot tube. The “Ref (-)” pressure port on the Meter connects to the black hose
from the static pressure connection of the pitot tube. The tubing open to ambient conditions press and hold “Hold/Zero” for
2 seconds to zero out the display.
• When make the measurement, the pitot tube tip should against the measured wind as shown in upper gure, and ensure
that the axis of the duct is aligned with the uid ow for ±10°. If Measure Velocity measures negative and show “Error” on
the display, check to make sure that the hoses are attached to the correct ports on the Meter and the pitot.
5-13. Measuring Flow
• Press “P/V/F” to enter air ow mode and press “Unit ” to select unit ..
• The Meter shows the duct shape and size. The Meter stores the last duct shape and size that is entered. If the duct is
different than the stored version, press “Setup ” button to nd the proper duct type for the measurement (rectangular or
round). Refer to Step duct shape and parameters setting .. (“Changing Setup Options.”)
Note: HOLD, Save, MIN/MAX/AVG, Zero, and Setup can be used when measuring pressure, velocity and ow.

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5-14. Displaying Temperature
Ambient temperature is displayed on the secondly show as a reference. The temperature can be displayed in either °C or °F.
Press “Unit ” to select unit °C or °F.
5-15. Holding the Displayed Readings
• Press “Hold/Zero” to freeze the readings on the display .The display shows HOLD.
• Press “Hold/Zero” again to turn off the HOLD function
5-16. Viewing the MIN, MAX, and AVG Readings
• Press “MAN/MIX” to step through the maximum (MAX), minimum (MIN), or the average (AVG) readings. The elapsed time
since entering MAX/MIN/AVG mode, or the time at which the minimum or maximum occurred appears on the display.
• Press “P/V/F” to show the maximum, minimum, and average of pressure, velocity or ow, and temperature value.
• Press “MAN/MIX” button for 2 seconds to exit MAX/MIN/AVG mode.
5-17. Saving Samples
The Meter saves various samples in its three major modes. To save a sample, do the following:
• When taking a sample, press “Save/Clear’’ to store the sample. The Meter can save up to 99 samples in each of its three
modes.
• If the memory is full (99 samples have been stored), more samples cannot be stored. If the user attempts to store another
sample, the Meter shows “FU” and does not save new readings.
5-18. Recall and Clearing Sample Data
• The Meter stores data that sometime will need to be recall and periodically to be cleared. Individual samples or the entire
data memory can be cleared. When the memory is full (99 samples), it shows ”FU” (Full) on the display when “Save/
Clear’’ is pressed and the Meter emits short beeps and will not save any value unless some samples are cleared.
To recall sample data, do the following:
• Press “P/V/F” to recall samples for that mode.
• Press “Avg/Rec” (RECALL)and hold the button for 2 second to recall samples. The last measurement saved appears rst.
Use “Unit ” and “Unit ” to locate the desired sample.
• Once the samples are taken, press “Avg/Rec” to view the average of all the samples.
• Press “Avg/Rec” and hold the button for 2 second to exit recall mode.
To clear individual sample data, do the following:
• Press “P/V/F” to recall samples for that mode.
• Press “Avg/Rec” (RECALL) and hold the
button for 2 second to recall samples. Use
“Unit ” and “Unit ” to select the desired
sample.
• Press “Save/Clear’’ to clear the sample.
Note that the number of samples displayed
is reduced.
• Press “Avg/Rec” and hold the button for 2
second to exit recall mode. To clear all sample
data, Refer to Step clear memory setting ..
(“Changing Setup Options.”)

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5-19. Error Codes
An error message will appear on the display if the meter fails an internal diagnostic test. And it will freeze all the buttons.
OL: Pressure or air velocity value is over the range.
-OL: Pressure value is below the range.
Error: air velocity or air ow is below the range.
5-20. Replacing the Batteries
• Turn off the thermometer if necessary.
• Loosen the screw and remove the battery door.
• Replace 9V batteries.
• Replace the battery door and tighten the screw.
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