Extech Instruments 421504 User manual

User's Guide
Dual Input RTD Thermometer
Model 421504
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com
99 Washington Street
Melrose, MA 02176
Fax [phone]
TestEquipmentDepot.com

Model 421504 Version 1.9 December 20043
Specifications
General Specifications
Display 5-digit LCD with overload/open-input indication
Over-range and open input Dashes are displayed in place of a temperature reading
Power Supply 9V battery
Battery life 100 hours typical with carbon zinc battery
Auto Power Off Meter turns off automatically after 30 minutes
Safety CE approved and water resistant meter housing
Weight 11.73oz. (365 g)
Dimensions 7.56 x 3.58 x 2" (192 x 91 x 52.5mm)
Accessories supplied 9V battery, RTD connectors (2), and protective holster
Range Specifications
Display Resolution 0.2oF or 0.1oC Resolution
RTD Probe (Pt 385 100Ω)-328 to 1472oF (-200 to 800oC)
(European curve Alpha = .00385)
RTD Probe (Pt 3926 100Ω)-328 to 1166oF (-200 to 630oC)
(U.S. curve Alpha = .003926)
Temperature units Selectable C or F temperature units
Accuracy is specified for operating temperatures in the
range of 64 to 82oF (18 to 28oC) for a period of one
year, not including the RTD probe error
±(0.05% rdg + 0.2oC) for oC Scale
Accuracy
±(0.05% rdg + 0.4oF) for oF Scale
Temperature Coefficient Multiply the applicable accuracy specification per oC
from 0 to 18oC and 28 to 50oC (32 to 64oF and 82 to
122oF) by 0.1
Input Protection 24VDC or 24VAC rms max. input on any combination
of inputs.
NOTE: Max. Voltage between T1 and T2 during
measurement = 1V
Reading rate One reading per second
Input connectors Accepts standard 3-terminal RTD sub-miniature
connectors (flat blade, 7.9mm spacing)
Ambient Operating Range 32 to 122oF (0 to 50oC); less than 80% RH
Storage Temperature -4 to 140oF (-20 to 60oC); less than 70% RH

Model 421504 Version 1.9 December 20044
Meter Description
1. RTD probe inputs
2. LCD multifunction display
3. Keypad
4. Protective holster
Note that the tilt stand and battery compartment are located on the back of the meter
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com

Model 421504 Version 1.9 December 20045
Display Description
Keypad Description

Model 421504 Version 1.9 December 20046
Operation
Connecting RTD Probes
1. This meter uses 3-wire RTD probes (available through Extech Instruments). Insert one
or two RTD probes to the top of the meter. The meter is supplied with two RTD probe
connectors.
2. When the meter is turned on, the temperature readings will appear on the LCD display.
3. If a probe is not inserted, improperly connected, or is malfunctioning, all dashes "------"
will appear in the temperature display area.
Meter Power
1. Ensure that a fresh 9V battery is properly installed in the meter.
2. The POWER button is used to turn the meter ON or OFF.
3. If the low battery indicator appears on the display, change the 9V battery.
RTD type selection
1. Select the RTD type (alpha curve 3850 or 3926) that is connected to the T1 terminal
using the Pt385/3926 button (the button with the number ‘5’ overlay).
2. Select the RTD type (alpha = 3850 or 3926) that is connected to the T2 terminal using
the Pt385/3926 button (the button with the number ‘0’ overlay).
3. The LCD display indicates which alpha curve is selected.
Note: Alpha curve 385 is the DIN/IEC worldwide current standard while Alpha 3926 is
an older standard. If unsure, check with the Probe manufacturer. If still in doubt, use
the 385 selection. The meter remembers the selection when powered OFF.
Selecting T1, T2, and T1-T2 Displays
1. Use the T1 T2 T1-T2 button (button with the number ‘4’ overlay) to select views for the
Primary display. RTD 1 (T1), RTD 2 (T2) or the difference between the two (T1-T2) can
be shown in the Primary display area.
2. Use the T1 T2 T1-T2 button (button with the ‘-’ overlay) to select views for the
Secondary display. RTD 1 (T1), RTD 2 (T2) or the difference between the two (T1-T2)
can be shown in the Secondary display area.
3. The LCD displays T1, T2, or T1-T2 icons for both Primary and Secondary displays for
convenience.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com

Model 421504 Version 1.9 December 20047
Temperature units – Degrees oC or oF
The Primary and Second display (one for each RTD input) can read in either degrees oC or
oF. Press the C/F button to toggle between oC and oF temperature units. The meter
remembers the selected unit of measure the next time the meter is used.
Data Hold
To freeze the LCD display, press the HOLD button. The HOLD icon will appear on the
upper right-hand side of the LCD. Press the HOLD button again to return to normal
operation (the HOLD display icon will switch off).
MIN, MAX, AVG Function with Timer (for Primary display only)
In the MIN/MAX/AVG mode of operation the meter tracks the highest (MAX), lowest (MIN),
and average (AVG) primary display readings for easy recall.
1. To enter this mode, press the MIN/MAX button (the RECORD display icon will appear).
Use the MIN/MAX button to cycle through MIN, MAX, and AVG modes each with its
own LCD display icon.
2. Each time a new MAX or MIN is detected, the previous MAX or MIN displayed value is
replaced and an audible tone will sound.
3. Use the HOLD button to start and stop recording. When recording is stopped, the
stored values are held in meter memory until the MIN/MAX/AVG mode is exited or
resumed (resume by pressing the HOLD button again).
4. The AVG mode keeps a true running average of temperatures recorded since the
MIN/MAX button was first pressed (up to a maximum of 22 hours). If 22 hours elapse
the average stored at this point is held on the display and is no longer updated (the
MIN and MAX functions continue without interruption indefinitely). If an overload is
recorded, the AVG function is halted and the AVG display shows "-------".
5. In this mode, the Primary displayed value is the MIN, MAX, or AVG reading depending
upon which icon appears on the LCD.
6. Each value for MIN/MAX/AVG has an associated time value (bottom right) indicating
when the displayed reading was taken. Set the timer clock in the SET mode (refer to
the SET MODE section).
7. The MIN/MAX/AVG mode cancels the Auto Power OFF feature, disables most of the
meter keys, and will not allow a manual power OFF. Press and hold the MIN/MAX key
for several seconds to exit MIN/MAX/AVG mode and return to normal operation.
Relative Mode (for Primary display only)
The Relative Mode permits the user to store a temperature and compare it to subsequent
temperature readings. In Relative mode the primary display indicates the actual
temperature minus the relative temperature. The user can store the current primary
temperature reading as the relative temperature or a temperature can be entered
manually. To manually enter a relative temperature, refer to the SET MODE section.
To enter the relative mode, press the REL button; The REL icon will appear on the LCD
and the temperature display will show zero (indicating that the actual and relative
temperatures are the same). Press the REL key again to exit the REL Mode.

Model 421504 Version 1.9 December 20048
SET MODE Programming
•Manually setting the Relative Values
Press the SET button once and the display will show all dashes "======". Enter the
relative value using the meter's buttons which double as numerical keys. Once the
Relative value is entered, press the ENTER key FOUR times to return to normal
operation. Now when the Relative Mode is activated, the Meter will display Actual
Temperature minus Relative Temperature. Refer to the Relative Mode section for more
details.
•Setting the Timer/Clock
1. To enter this mode, press the SET button and then the ENTER button.
2. Program the Hours, Minutes, and Seconds (HH:MM:SS) using the overlay numeric
buttons.
3. Press the ENTER button three times to return to normal meter operation. The clock
will begin running.
•Alarm HI/LO Limit Programming
1. Press the SET button once and then the ENTER button twice.
2. Program the desired HI Alarm value (temperature at which the meter will audibly
alert the user) using the overlay numerical keys (alarm values are four number
digits; 80° should be entered as 0080; 100° as 0100, etc.).
3. Press the ENTER button once.
4. Program the LO Alarm Limit value (temperature at which the meter audibly alerts the
user).
5. Press the ENTER button once to return to normal operation. The alarms will be
armed giving an audible alert when a limit is reached.
6. When the actual temperature meets or exceeds the user programmed temperature
limits a continuous alert tone will be heard. Press the HI/LO Limits button to silence
the alarm when it audibly trips.
Automatic Power OFF
The meter is equipped with an automatic power off utility. After 30 minutes the meter
automatically shuts off unless the meter is in the SET, RELATIVE, or MIN/MAX/AVG
mode. Note that in the SET, RELATIVE, and MIN/MAX/AVG modes the meter cannot be
shut off manually either; exit these modes before attempting to turn the meter OFF.
Battery replacement
When the low battery indicator appears (or when the LCD does not switch on when the
POWER button is pressed), replace the 9V battery.
1. Remove the rubber protective meter jacket
2. Remove the two Phillips screws and remove the battery compartment cover
3. Replace the 9V battery and reassemble the meter.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com