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Model GL840 with 60-V Isolation

20 to 200-channel Handheld Voltage and Thermocouple Data Logger

International shipping not available for this product
  • Includes a GL840-M data logger, an AC adapter, and software on CD (Ship to USA only)
  • 20 analog input channels, expandable to 200
    • Programmable per channel
    • ±20 mV to ±100 V over 12 ranges
    • Supports direct-connected thermocouples of any type
    • Supports direct-connected PT100/PT1000 RTDs
    • Full isolation per channel (60V)
  • 4 discrete input channels
    • Programmable as a group as logic or pulse inputs
    • Pulse inputs support counter or frequency inputs
  • 4 discrete alarm outputs
  • Optional WiFi wireless operation
  • Flexible triggering
  • Built-in, 7-inch color display
  • Built-in Web server operation for remote operations
  • Removable SD memory support up to 32 GB capacity
  • Includes 4 GB of internal non-volatile memory
  • Operates either stand-alone or PC-connected
  • PC-side software included
  • Factory-calibrated. NIST-traceable certificates available in Accessories tab
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GL840 DAQ and Data Logger
This data logger features 20 analog input channelsThis data logger system has four digital inputs and four digital outputsThis data logger can sample and record data 10ms to 10 second intervals.This data logger system is expandable to 200 channels
This data logger has a USB interfaceThis data logger has an Ethernet interfaceThis data logger can save data directly to a USB flash drive
Get same day shipping when you order this data logger before 3PM ETThis data acquisition system has a 30-day Money back guarantee


GL840 Voltage and Thermocouple Data Logger system features 20 isolated analog input channels (expandable to 200), 4 discrete inputs, and 4 discrete outputs with extremely flexible triggering conditions. Use the GL840 either stand-alone with a built-in battery compartment or pc-connected via the USB or Ethernet port.

Model GL840 Series is a third-generation data logger product with exceptional price/performance. It’s a 20 analog channel device expandable to 200 channels, augmented by four discrete inputs and outputs. Its discrete inputs can be configured as a group to be either logic inputs or pulse inputs. When configured for pulse, each of the four channels can be configured to measure frequency or to count. The four discrete outputs are alarms that can be triggered by a variety of easily-defined analog and pulse/discrete input channel conditions. The 20 GL840 analog input channels may each be configured to measure a direct connected voltage in the range of 20 mV to 100 V full scale across 12 ranges, a direct-connected thermocouple of any type, or a 3-wire PT100 or PT1000 RTD. Each of the GL840’s analog input channels is electrically isolated from other channels and from power ground allowing off-ground measurements using shunts, as well as powered or grounded thermocouples. Model GL840-M supports up to 60 Vp-p common mode. The most powerful GL840 feature is its triggering flexibility. Data recording can be independently started or stopped as a function of analog and pulse/discrete signal level (single or windowed), alarm, date and time, and day-of-the-week. Triggers can also be configured to operate only once, or to automatically repeat. The ability of the GL840 to adapt to virtually any desired trigger condition allows the instrument to operate unattended for long periods of time with complete autonomy.

The GL840 operates either connected to a PC or entirely stand-alone. Connection to a PC may be over a standard Ethernet, USB, or optional wireless connection. Each connection approach may take advantage of supplied PC-side software to configure, acquire, display, and record digitized information for storage directly to the PC’s HDD. Acquired data may be retrieved for review and analysis after recording, including the ability to export to Microsoft Excel. Using the GL840’s built-in Ethernet port or wireless option enables the instrument’s networking features, allowing it to be remotely configured and managed using the standard Web browser of any computer or smart phone. The GL840 is provided with 4 GB of non-volatile memory embedded inside the instrument. The instrument supplies an external SD card slot for additional storage if needed.

The measurement reach of the GL840 is further extended by use of GS Sensor accessories that can be either connected directly to the GL840 or wirelessly accessed with the B-568 wireless option using the GL100-WL. Extended measurements of temperature/humidity, acceleration, CO2, illuminance, ac current, and more are available using GS Sensors.



4-20mA Current Loop Shunt Resistor

$ 2.99
R250 Shunt Resistor


250 Ω ±0.1% Precision, Metal Film, 1/2W, Axial Resistor
Exceptionally low noise; typically 0.10 μV/V
Low voltage coefficient to ±5 ppm/V
Flame retardant coating. RoHS compliant. Learn More


Calibration Certificate

NIST Calibration Certificate for Graphtec Data Loggers


NIST-traceable calibration certificate for all Graphtec GL240 and GL840 Data Loggers. Does not include data. This item is NOT included with a new unit and should be purchased at the same time as the new unit. Shipping charges will apply if not ordered at time of logger purchase. Learn more about Calibrating your device.


Calibration Certificate

NIST Calibration Certificate for Graphtec Data Loggers


NIST-traceable calibration certificate for all Graphtec GL240 and GL840 Data Loggers. Includes data. This item is NOT included with a new unit and should be purchased at the same time as the new unit. Shipping charges will apply if not ordered at time of logger purchase. Learn more about Calibrating your device.


Calibration Certificate

ISO 17025 Calibration Certificate for Graphtec Data Loggers


ISO:17025 calibration certificate for all Graphtec GL840 Data Loggers. Includes data. This item is NOT included with a new unit and should be purchased at the same time as the new unit. Shipping charges will apply if not ordered at time of logger purchase. This item DOES NOT ship same-day. Please allow 4 week lead time. Learn more about Calibrating your device.


Logic/Alarm Cable

B-513 Graphtec Logic Alarm Cable


2-meter logic/alarm cable with bare tips.


DC Power Cable

B-514 Graphtec DC Power Cable


2-meter DC power cable with bare tips.


Battery Pack

B-569 Graphtec Battery Pack


One (1) 7.2V/2900mAh lithium battery pack. Please Note: Continental U.S. shipping ONLY.


Humidity Sensor

B-530 Graphtec Humidity Sensor


3-meter humidity sensor with dedicated power connector. Learn More.


Input Terminal

B-564 Input Terminal


20-channel standard input terminal for GL840 data loggers. Please note: Use of one or more B-564 input terminals with the GL840-WV forces all channels to the low common mode voltage spec of 60V. Use model B-565 to maintain the 300V spec across all channels.


Extension Terminal Base

B-566 Extension Base


Extension terminal base for GL840 data loggers. Includes base unit, connection plate, and screws.


Extension Terminal Cable

B-567-05 Extension Cable


50 cm extension terminal cable for GL840 data loggers.


Extension Terminal Cable

B-567-20 Extension Cable


2 m extension terminal cable for GL840 data loggers.


WiFi Coupler

B-568 Wifi Coupler


Wireless communication option for GL240 and GL840 data loggers. 802.11/b/g/n. Required for use with GL100-WL Data Logger with a GL240. Attachment of this wireless option to the instrument prevents the use of an external SD memory card, with only the internal 4 GB non-volatile memory available for data storage.



B-536 Graphtec Carrying Case


Carrying Case. Interior padding and rugged exterior for safe transportation of your GL840 data logger.


DIN Adapter

B-570 Graphtec DIN rail mounting adapter


DIN Rail Mounting Adapter for models GL840-M and GL840-WV.

Wireless Logger and Sensors


Temperature Sensor

Thermistor temperature sensor


Thermistor Temperature sensor connects to model GS-4TSR. Measures -40 to 105 °C.


Temperature Sensor

Thermistor temperature sensor


Thermistor Temperature sensor connects to model GS-4TSR. Ultra thin. Measures -40 to 120 °C.


Current Sensor

AC Current sensor


Clamp-on AC Current sensor for GS-DPA-AC. 50 A AC current.


Current Sensor

AC Current sensor


Clamp-on AC Current sensor for GS-DPA-AC. 100 A AC current.


Current Sensor

AC Current sensor


Clamp-on AC Current sensor for GS-DPA-AC. 200 A AC current.



File Conversion

FREE Graphtec to WinDaq High Resolution (GBD - to - WDH) File Conversion Utility (beta version) converts files recorded with a Graphtec device to WinDaq Playback for analysis.

Graphtec to WinDaq file converter

Graphtec Downloads

Data Logger Software

Visit the Support Download page at Graphtec for software (both links below take you to another site).

Graphtec Downloads


Analog Inputs
Number of Channels: Maximum 200ch available for 20ch/1 terminal or extension unit
GS sensor and terminal/adapter connection terminal: One module
Optional (GS sensor and terminal / adapter ) connections only
Data backup functions: Setup parameters: EEPROM
Clock: Lithium battery
Clock accuracy:
(23°C environment)
±0.002% (accurate within about 50 seconds per month)
Operating environment: 0 to 45°C, 5 to 85% RH
(0 to 40°C when operated in batteries/15 to 35°C when battery is charging)
Withstand voltage: Between each input ch and GND terminal: 350Vpp 1 minute
Between each input terminals: 350Vp-p 1 minute
Power supply: AC adapter: 100 to 240 VAC, 50 to 60 Hz
DC input: 8.5 to 24 VDC (26.4 V max.)
Battery pack (option): 7.2 VDC (2900 mAh), two packs can be mounted
Power Consumption: AC Power consumption (when AC adapter is used)
Condition Normal Consumption Consumption during battery recharge
LCD on 24 VA 38 VA
Screensaver on 19 VA 33 VA

DC Power consumption
DC Voltage Condition Normal Consumption Consumption during battery recharge
+24V LCD on 0.36 A 0.65 A
+24V Screensaver on 0.27 A 0.56 A
+12V LCD on 0.70 A Cannot Recharge
+12V Screensaver on 0.50 A Cannot Recharge
+8.5V LCD on 1.00 A Cannot Recharge
+8.5V Screensaver on 0.70 A Cannot Recharge

*Set the LCD to “Bright” as normal condition.
External Dimensions: 240×158×52.5mm (not including protruding parts)
Weight: 1010g (AC adapter and battery are not included, but one terminal unit is included)
Vibration-tested conditions: Equivalent to automobile parts Type 1 Category A classification
Memory devices
Memory capacity: SD CARD Slot: 2 (Compatible with SDHC, up to approx. 32GB memory available)
• Approx. 4GB internal, non volatile memory
• Possible to save up to 2GB for one file
Memory contents: Setup conditions, Measured data, Screen copy
Interface types: Ethernet (10BASE-T/100BASE-TX)
USB 2.0
Wireless LAN (Option)
Functions: Data transfer to the PC (realtime, SD memory card data)
PC control of the GL840
Control of wireless sensor GL100GL100-WL, Data capture (when connected to the wireless LAN: up to 5 units)
Ethernet functions:
Web server functions: Displays the screen images.
FTP server function: Transfer and delete the captured data in the SD memory card.
FTP client function: Back up the captured data to the FTP server.
NTP client function: Time-synchronize the NTP server.
DHCP client function: IP address automatic acquisition
DHCP client function : Automatically retrieves the IP address
E-mail function: Send and receive the e-mail
USB functions: USB drive mode: Transfer and delete the captured data in the SD memory card.
Realtime data transfer speed: 10 ms/1 ch maximum (dependant on number of channels).
Display: 7-inch TFT color LCD (WVGA: 800 × 480 dots)
Displayed languages: Japanese, English, French, German, Chinese, Korean, Russian, Spanish
Backlight life: 50,000 hrs (until the brightness is reduced to 50%), It varies with operating environment
Backlight: Screen saver function provided (10, 30 sec., 1, 2, 5, 10, 30, 60 min.)
Input Unit Specifications
Number of input channels: 20ch (200ch available when used with the extension terminal base). Possible to direct-connect or connect with the extension terminal connection cable (sold separately) between the GL840 and terminal unit, or between terminal units.
Input terminal type: M3 screw type terminals (Rectangular flat washer)
Input method: Photo MOS relay scanning system
All channels isolated, balanced input
Terminal b to be used to connect the resistance temperature detector is shorted within all channels.
Scan speed: 10 ms/1 ch maximum
Measurement ranges: Voltage: 20, 50, 100, 200, 500 mV; 1, 2, 5, 10, 20, 50, 100 V; 1-5 V F.S.
Thermocouples : K, J, E, T, R, S, B, N, W (WRe5-26)
Resistance temperature detector: Pt100, JPt100, Pt1000 (IEC751)
Temperature range : 100°C, 500°C, 2000°C (150°F, 750°F, 3000°F)
Humidity: 0 to 100% (voltage 0 to 1 V scaling conversion) fixed (requires B-530)
Measurement accuracy:
23°C ±5°C; When 30 minutes or more have elapsed after power was switched on;
Sampling 1 s/10 ch;
Filter ON (10);
GND connected
Voltage: 0.1% of F.S.
Temperature Thermocouple
TC Type Measurement Temperature Range (°C) Measurement Accuracy (°C)
R/S 0 ≤ TS ≤ 100
100 < TS ≤ 300
R : 300 < TS ≤ 1600
S : 300 < TS ≤ 1760
± (0.05% of rdg +2.0)
± (0.05% of rdg +2.0)
B 400 ≤ TS ≤ 600
600 < TS ≤ 1820
± (0.05% of rdg +2.0)
K -200 ≤ TS ≤ -100
-100 < TS ≤ 1370
± (0.05% of rdg +2.0)
± (0.05% of rdg +1.0)
E -200 ≤ TS ≤ -100
-100 < TS ≤ 800
± (0.05% of rdg +2.0)
± (0.05% of rdg +1.0)
T -200 ≤ TS ≤ -100
-100 < TS ≤ 400
± (0.1% o f rdg +1.5)
± (0.1% o f rdg +0.5)
J -200 ≤ TS ≤ -100
-100 < TS ≤ 100
100 < TS ≤ 1100
± (0.05% of rdg +1.0)
N -200 ≤ TS < 0
0 ≤ TS ≤ 1300
± (0.1% o f rdg +2.0)
± (0.1% o f rdg +1.0)
W 0 ≤ TS ≤ 2000 ± (0.1% o f rdg +1.5)
Reference contact compensation accuracy ±0.5

* Thermocouple diameters T, K: 0.32 φ, others: 0.65 φ
Resistance temperature detector:
Type Measurement Temperature Range (°C) Applied Current Measurement Accuracy (°C)
Pt100 -200 to 850 (FS=1050) 1mA ±1.0
JPt100 -200 to 500 (FS=700) 1mA ±0.8
Pt1000 -200 to 500 (FS=700) 0.3mA ±0.8

*3-wire system
Temperature Range:
Type Temperature Range (°C F.S.) Resolution Measurement Range (°C)
R/S 100 0.01 0 to 100
500 0.05 0 to 500
2000 0.1 R: 0 to 1600
S: 0 to 1760
B 500 0.05 400 to 500
2000 0.1 500 to 1820
K/E/T/J/N 100 0.01 -100 to 100
500 0.05 K/E/J/N: -200 to 500
T : -200 to 400
2000 0.1 K : -200 to 1370
E : -200 to 800
T : -200 to 400
J : -200 to 1100
N : -200 to 2000
W 100 0.01 0 to 100
500 0.05 0 to 500
2000 0.1 0 to 2000
Pt 100 0.01 -100 to 100
500 0.05 -200 to 500
2000 0.1 Pt100: -200 to 850
JPt100/Pt1000: -200 to 500

*Measurement accuracy does not change due to the temperature range
Reference contact compensation accuracy: Internal/External switching
A/D converter: Method :ΔΣ method
Resolution :16-bit (Effective resolution: About 1/40,000 of the +/- range)
Temperature coefficient: Gain: 0.01% of F.S./°C
Zero: 0.02% of F.S./°C (Occurs when sampling speed is 10, 20, or 50 ms.)
Input resistance: 1 MΩ ±5%
Allowable signal source resistance: Within 300Ω
Maximum permissible input voltage: Between +/– input terminals: 20mV to 1V range (60Vp-p); 5V to 100V range (110Vp-p)
Between input terminal/input terminal: 60 Vp-p
Between input terminal/GND: 60 Vp-p
Withstand voltage: Between input terminal/input terminal: 350 Vp-p 1 minute
Between input terminal/GND: 350 Vp-p 1 minute
Insulation resistance: Between input terminal/GND: 50MΩ or more (at 500 VDC)
Common mode rejection ratio: 90 dB or more (50/60 Hz; signal source 300Ω or less)
Noise: 48 dB or more (with +/– terminals shorted)
Filter: Off, 2, 5, 10, 20, 40
Filter operation is on a moving average basis.
The average value of the number of set samples is used.
If the sample interval exceeds 30 seconds, the average value of data obtained in a sub-sample (30 seconds) is used.
Function Specifications
Display screen: Waveform + Digital screen, All Waveform screen, Digital + Calculation Display screen, Expanded digital screen
* Can be switched using the dedicated key (toggle operation)
* For the Expanded Digital screen, the number of channels and the display channel must be specified
* The waveform is not rewritten due to the change of the TIME / DIV.
Sampling interval: 10 ms/1 ch maximum (GBD/CSV-formatted)
10, 20, 50, 100, 125, 200, 250, 500 ms; 1, 2, 5, 10, 20, 30 sec.; 1, 2, 5, 10, 20, 30 min.; 1 hour
* The settings of 125 ms or below can be used depending on the input settings and the measuring channel.
EU (scaling function): 4 points can be set for each channel
The temperature range scaling function is available.
Functions during capture: Confirmation of the captured data
Saving of data between cursors
Replacement of the SD memory card
* When the wireless sensor (GL100-WL) is connected, the sample interval among 10, 20, and 50ms cannot be replaced during recording.
Data save function: Capture destination: SD memory card (Available both slot 1 and 2)
Captured data: Settings, Screen data, Measurement data
Capture function: Function: OFF, Ring recording, Relay recording
Ring recording: Number of recording points: 1000 to 2000000
When ring capture is ON, the memory space that can be used for capture is one-third of the free space
Relay recording: The data is continuously recorded in 2GB-separated files without missing data.
Replaying data: GBD/CSV-formatted data file (only data captured in this GL840)
Calculation between channels: Calculation type: Four arithmetic operations (+, -, ×, ÷)
Target input: Analog CH1 to CH200
GS sensor and terminal/adapter: CH1 to CH8
Wireless sensor: CH1-1 to CH5-8
Statistical calculation: Statistical calculation type: Average value, peak value, maximum value, minimum value, root mean square value
Number of calculations: Two arithmetic operations can be set to each channel
Calculation method: Real-time calculation and specified between cursors (during replay)
* Real-time calculation results are displayed on the Digital screen + Calculation Display screen.
Search functions: Function: Search the captured data for the required number of points
Search type: Channel Pulse, Logic, Level, Alarm search
Annotation input function: Function: A comment can be entered for each channel
Input table characters: Alphanumerics
Number of characters: 31
(The number of characters can be displayed on the screen is up to eight characters.)
Navigation function: Easy capture measurement, easy trigger setting, wireless LAN setting functions
Trigger/Alarm Functions
Repeat Trigger: Off, On
Trigger types: Start: Data capture starts when a trigger is generated
Stop: Data capture stops when a trigger is generated
Trigger conditions: Start: Off, Level, Alarm, External, Time
Stop: Off, Level, Alarm, External, Time
Trigger judgment modes: Combination: Level OR, Level AND, Edge OR, Edge AND
Analog channel judgment mode: H (↑), L (↓), Window In, Window Out
Logic channel judgment mode: H (↑), L (↓)
Pulse channel judgment mode: H (↑), L (↓), Window In, Window Out
Alarm judgment modes: Combination: Analog, Logic or “AND” / “OR” of pulse
Analog judgment: H (↑), L (↓), Window In, Window Out
Logic judgment: Pattern
Pulse judgment: H (↑), L (↓), Window In, Window Out
External Input/Output Functions
Input/output types: Trigger input (1 ch) or External sampling input (1 ch)
Logic input (4 ch) or Pulse input (4 ch)
Alarm output (4 ch)
* Switch between Logic and Pulse
* Switch between Trigger and External sampling.
* The Input/output cable for GL B-513 (option) is required to use the external output function.
Input specifications: Input voltage range: 0 to +24 V (single-ended ground input)
Input signal: No-voltage contact (a-contact, b-contact, NO, NC), Open collector, Voltage input
Input threshold voltage: Approx. +2.5 V
Hysteresis: Approx. 0.5 V (+2.5 to + 3 V)
Alarm output specifications: Output format: Open collector output (5 V, pull-up resistance 10KΩ)
<Maximum ratings of output transistor>
• Collector-GND voltage: 30 V
• Collector current: 0.5 A
• Collector dissipation: 0.2 W
Output conditions: Level judgment, window judgment, logic pattern judgment, pulse judgment
Pulse input: Revolutions mode (engines, etc.): Counts the number of pulses per sampling interval, and converts them to RPM. Set the number of pulses per revolution during revolution. Spans : 50, 500, 5000, 50 k, 500 k, 5 M, 50 M, 500 M PRM/F.S.
Counts mode (electric meters, etc.): Counts the number of pulses for each sampling interval from the start of measurement. Spans : 50, 500, 5000, 50 k, 500 k, 5 M, 50 M, 500 M C/F.S.
Inst. mode: Counts the number of pulses for each sampling interval. Resets the count value after each sampling interval. Spans : 50, 500, 5000, 50 k, 500 k, 5 M, 50 M, 500 M C/F.S.
Maximum input frequency: 50kHz
Maximum number of count: 50kC/sampling (16-bit counter)
Connectable sensor, terminal, adapter: Number of GS sensors and terminals/adapter connection terminals: 1
Generic name: GS sensor and terminal/adapter GS-TH: Temperature and humidity sensor
GS-4TSR: 4CH thermistor terminal
GS-LXUV: Illuminance / ultraviolet sensor
GS-DPA: Branch adapter for GS
GS-DPA-AC: Adapter for AC current sensor
GS-CO2: CO2 sensor
GS-3AT: 3-axis acceleration / temperature sensor
GS-4VT: 4CH voltage / temperature terminal
* The items above are optional accessories.
Sampling: 500 ms to 1 hour
* Specific setting is not required. It is synchronized to the setting of the GL840.
Control Software
Compatible OS: Windows8.1/Windows8/Windows7/Windows Vista
Function: Main unit control, realtime data capture, data conversion
Number of groups: 4 groups MAX
Number of CHs per group: Up to number of connected module
Max number of channels: 1000 ch maximun
Settings: AMP settings, capture settings, trigger/alarm settings, report settings, others
Captured data: Realtime data (CSV, GBD Binary)
Data in SD memory card (CSV, GBD binary)
Display: Analog waveforms, logic waveforms, pulse waveforms, digital values
Display modes: Y-T View, Digital View, X-Y View between Cursors (only during replay)
File conversion: Between cursors, All data
Monitor functions: Alarm monitor enables sending of email to the specified address
Statistic/History: Displays max, min and average values
Report function: Enables creation of daily or monthly files
E-mail function: E-mail sent to specified address on alarm


Graphtec GL820 Playlist
GL820 Setup

View the GL820 Data Logger setup tutorial playlist on YouTube.
Graphtec APS Software Overview
Graphtec APS Software

APS PC-based software provides access to all the features on the front panel, and more.

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Model Analog
Expandable* Measurement
Max Sample
Rate (Hz)
Interface Data Storage Price
DI-2008 8 Yes A Yes 200 16 7 Bi USB PC $499
DI-808 8 - A Yes 40 16 4 In 4 Out Ethernet Internal, USB flash, Cloud $995
DI-4718B-U 8 - C Yes (DI-8B) 160,000 12 to 16 2 In USB PC or USB flash $795
DI-4718B-E 8 - C Yes (DI-8B) 160,000 12 to 16 2 In USB, Ethernet PC or USB flash $695
GL240 10 - B Yes 100 16 4 In 4 Out USB PC, USB flash, Internal, Cloud $995
GL840-M 20 Yes B Yes 100 16 4 In 4 Out USB, Ethernet PC, USB flash, Internal, Cloud $2345
DI-718B-US 8 - C Yes (DI-8B) 14,400 14 2 In USB PC or SD Card $695
DI-718B-ES 8 - C Yes (DI-8B) 14,400 14 2 In Ethernet PC or SD Card $895

*Expansion capabilities dependent on model.

Use the following chart to determine Measurement Ranges:

A B C*
±10 mV
±25 mV
±50 mV
±100 mV
±250 mV
±500 mV
±1 V
±2.5 V
±5 V
±10 V
±25 V
±50 V
±20 mV
±50 mV
±100 mV
±200 mV
±500 mV
±1 V
±2 V
±5 V
±10 V
±20 V
±50 V
±100 V
1-5 V
±10 mV
±50 mV
±100 mV
±1 V
±5 V
±10 V
±20 V
±40 V
±60 V

*Dependent on 8B module.