Extech 421509 7 Thermocouple Dual Input Datalogger with Alarm


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Extech 421509 7 Thermocouple Dual Input Datalogger with Alarm Memory stores up to 16 data sets, 1024 maximum data capacity.



  • Seven Thermocouple type selections available: K, J, T, E, R, S, N. Comes as standard with two Type-K bead wire temperature probes (-4 to 482°F /-20 to 250° C) unless different thermocouple requested
  • Large backlit LCD with two secondary displays for simultaneous T1, T2, T1-T2, Time and advanced readouts
  • T/C offset adjustment
  • REC, MAX, MIN, MAX-MIN, AVG and °C/°F switchable
  • Data Hold and Relative Function
  • Built-in bi-directional RS-232 PC interface
  • Programmable Hi/Lo audible alarm
  • Real time clock with calendar
  • Selectable auto power off function, disable capability 

Thermocouple Dual Input Datalogger with Alarm Details

Detailed, accurate field temperature readings require an up-to-date thermocouple datalogger. The Extech 421509 7 Thermocouple Dual Input Datalogger with Alarm makes a fine choice for engineers and test professionals.

The Extech 421509 has pre-set sensitivities for seven of the ten primary thermocouple types: K, J, T, E, R, S and N. This combination gives it an effective operating range from -200 to 1700degC.

The Extech 421509 provides simultaneous display of two probe temperatures and their difference (T1, T2, T1-T2 readings) and time via a large backlit LCD display with two secondary displays. The display is switchable into centigrade or fahrenheit modes, and offers programmable alarms for HI and LO temperatures and for offsets on both T1 and T2. There's also a HOLD function and a REL mode for live assessment of temperature variations from a user-defined norm.

Used as a datalogger, the unit is even more versatile. It offers programmable time intervals and MAX, MIN, MAX-MIN, AVG, and REL functions. The Extech's on-board memory stores up to 16 sets of data, and can be easily connected to an external PC via its built-in RS-232 port.

At 365g, the Extech 421509 is lightweight and robust, with a high-visibility orange casing. Average battery life is 100 hours.

The device ships with a standard K (chrome/alumel) thermocouple and an RS-232 data cable. A Windows software package, also included, offers excellent logging capabilities and an inbuilt graphing function.


K type -328 to 2501°F (-200 to 1372°C) 0.1o (0.2°>700°F)
J type -346 to 2192°F (-210 to 1200°C) 0.1o (0.2o>500°F)
T type -328 to 752°F (-200 to 400°C) 0.1o (0.2o>600°F)
E type -346 to 1832°F (-210 to 1000°C) 0.1o (0.2o>450°F)
R type 32 to 3212°F (0 to 1767°C) 1o
S type 32 to 3212°F (0 to 1767°C) 1o
N type -58 to 2372°F (-50 to 1300°C) 0.2°F (0.1°C)
K, J, T, E types ±(0.05% rdg + 0.6°F) -58°F to 2501°F
±(0.05% rdg + 1.4°F) -58°F to -346°F
±(0.05% rdg + 0.3°C) -50°C to 1370°C
±(0.05% rdg + 0.7°C) -50°F to -210°C
N type ±(0.05% rdg + 1.6°F) -58°F to 32°F
±(0.05% rdg + 0.8°F) 32°F to 2372°F
±(0.05% rdg + 0.8°C) -50°C to 0°C
±(0.05% rdg + 0.4°C) 0°F to 1300°C
R, S types ±(0.05% rdg + 4.0°F) 32°F to 3212°F
±(0.05% rdg + 2.0°C) 0°C to 1767°C
Supplied Therm°Couples 4', type K (with teflon insulation) Max insulation temp: 500°F (260°C)
Accuracy ± 4°F (±2.2°C) or ± 0.75% °F rdg
(whichever is greater) from 32 to 1472°F (0 to 800°C)
Battery Life 100 hours typical
Dimensions/Weight 7.5x3.6x2.1” (192x91x52.5mm); 11.7oz. (365g)


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  • Extech 421509 7 Thermocouple Dual Input Datalogger with Alarm