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LJTick-Resistance

Stock: In Stock
Price: $25.00
LabJack LJTick-Resistance-1k Resistor Divider Accessory Compatible with LabJack USB, Ethernet, WiFi DAQ Devices

The LJTick-Resistance (LJT-Rx) makes it easy for LabJack devices to measure resistive sensors. This tick gives users a regulated 2.5V signal that can be used as a excitation voltage and a known resistance value in series with a sensor input line. This gives users the ability to calculate the resistance of their connected sensor.

  • Uses precision 1k, 10k, 100k, or 1M resistors in a resistor divider setup.

Common Applications

  • Measuring resistive sensors like RTDs.

Figure 1: LJTick-Resistance

Figure 2: LJTick-Resistance with U3-LV

Screw Terminal Descriptions

Vref: A 2.5 volt reference voltage output. Internally this reference is used for level shifting, but very little current is used, leaving substantial current available to the user if a very accurate 2.5 volt reference is needed.

GND: Same as LabJack ground (GND).

VINA/VINB: These are the LJTick-Resistance input terminals.


LJTick-Resistance Hardware Block Diagram

Figure 3: LJTick-Resistance Hardware Block Diagram

Note: The part labeled as the "Precision Resistor" is the 1k, 10k, 100k, or 1M precision resistor that varies between the LJTick-Resistance variants.



LJTick-Resistance Schematic

Figure 4: LJTick-Resistance Schematic

Note: The part labeled as the "Precision Resistor" is the 1k, 10k, 100k, or 1M precision resistor that varies between the LJTick-Resistance variants.


Specifications

For more specifications about the reference voltage IC and Op Amp used in the LJTick-Resistance look at the following datasheets:

2 comments

ezDAQ's picture

Feasible to Connect/measure Pt1000 for tempeature?

Can you please explain in detail for wiring  w/ pictures?

LabJack Support's picture

Yes, the LJTR-1k is recommended for RTDs.  In fact, it is our preferred method for RTDs:

https://labjack.com/support/app-notes/temperature-sensors

As of this writing, the documentation is not properly gathered for this.  The applicable information is still on the LJTick-Divider Datasheet where you want to see the section "Resistance Measurement with the ...":

https://labjack.com/support/datasheets/accessories/ljtick-divider

For wiring, simply connect one side of the RTD to Vref and the other side to VINA.

For the equations, R1+R2=0 on the LJTR, and if you have the LJTR-1000 then R3=1000, so the equations for the LJTick-Resistance-1k are:

Vout = Vref*1000/(Ru+1000)

Ru = ((Vref-Vout)*1000)/Vout

For a PT1000 you expect that it will be 1000.0 ohms at 0 degC and the resistance will change about 3.85 ohms/degC (most common coefficient).  Say room temperature is 22 degC and putting your fingers on the sensor warm it up to 25 degC.  At 22 deg C you expect 1084.7 ohms and at 25 degC you expect 1096.3 ohms.  If Vref is 2.50, the voltages you expect are:

22C => 1.199213V

25C => 1.192577V

Note that on the T7 there you can use the AIN-EF system to do the math, but the above is still useful for understanding and troubleshooting:

https://labjack.com/support/datasheets/t7/ain/extended-features/rtd