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LJTick-Divider Datasheet

Stock: In Stock
Price: $25.00
LabJack USB, Ethernet, WiFi DAQ Device Resistor Divider Accessory LJTick-Divider-DIV-4

LJTick-Divider

The LJTick-Divider (LJTD) is a signal-conditioning module designed to divide 2 single-ended channels of higher voltage analog signals down to 0-3.5 volt signals. The stock builds provide divisions of /4, /5, /10, and /25, and there is a -C custom option for user specified builds.  The use of large resistors and a precision op-amp buffer provide an input impedance of about 1 MΩ. By adding or replacing resistors, many other configurations are possible.

The 4-pin design plugs into the standard AIN/AIN/GND/VS screw terminal block found on all LabJacks except the original U12.  Note that the best performance on the U3 or T7 is achieved with low-voltage inputs (labeled FIO and EIO).

Figure 1: LJTick-Divider

Figure 2: LJTick-Divider With UE9

VINA/VINB: These screw terminals are for the 2 single-ended channels of input analog voltages.  Each voltage is multiplied by the fractional slope to provide a lower voltage to the LabJack.  Note that the outputs of the LJTD are limited to about 0-3.5 volts.

GND: Same as LabJack ground. VINA/VINB must be referred to this ground.

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.


Figure 3: Schematic For Each Channel

 

The above figure is a schematic for one channel of the LJTD, showing the standard factory installed values for UNI10V. The input/output relationship is described by the below equations, assuming the op-amp is in the default unity gain configuration.

General Equations for Figure 3:
Vout = Vin*Rpar/(R1+R2)  +  Rpar*Vref/R4
Slope = Rpar/(R1+R2)
Offset = Rpar*Vref/R4
Rpar = Rparallel = 1 / ( (1/(R1+R2) + 1/R3 + 1/R4) )

Simplified Equations for Unipolar Builds:
Vout = Vin*R3/(R1+R2+R3)
Slope = R3/(R1+R2+R3)

 

The resistors R1+R2, R3, and R4, can be changed to provide other ranges as shown in the table below.

The packages for resistors R1-R4 are 0805, while all other resistors and capacitors are 0603. The tolerance of the factory installed resistors is 0.05%, so a good option available from digikey.com is the Panasonic ERA-6ARW series.

The table shows the input voltage at an output voltage of 0.0 and 2.5 volts. It also shows the input voltage for an output voltage of 3.5 volts, as the internal buffer amplifier accepts a maximum input voltage of 3.5 volts when powered by VS=5.0 volts, and thus when the amp is configured for unity gain the maximum output voltage is 3.5 volts. The Slope and Offset columns go with the formula

VIN (OUT=0):  This is the input voltage that results in an output voltage of 0.0 volts.  The typical minimum output voltage of the LJTD is about 0.001 volts.

VIN (OUT=2.5):  This is the input voltage that results in an output voltage of 2.5 volts.

VIN (OUT=3.5):  This is the input voltage that results in an output voltage of 3.5 volts.  The typical maximum output voltage of the LJTD is VS-1.5 which is about 3.5 volts.

Vout = Slope*Vin + Offset.

Table 1. Ranges for divider circuit with different R1-R4

R1+R2 R3 R4 Slope Offset VIN (OUT=0) VIN (OUT=1.0) VIN (OUT=2.5) VIN (OUT=3.5)
[ohms] [ohms] [ohms] [volts/volts] [volts] [volts] [volts] [volts] [volts] Name
720k 240k 0.25 0 0 4.0 10.0 14.0 -4
720k 180k 0.2 0 0 5.0 12.5 17.5 -5
900k 100k 0.1 0 0 10.0 25.0 35.0 -10
876k 36.5k 0.04 0 0 25.0 62.5 87.5 -25
720k 680k 0.4857 0 0 2.1 5.1 7.2 UNI5V
360k 240k 0.4 0 0 2.5 6.3 8.8 UNI6V
720k 240k 0.25 0 0 4.0 10.0 14.0 UNI10V
720k 220k 0.234 0 0 4.3 10.7 15.0 UNI11V
720k 100k 0.122 0 0 8.2 20.5 28.7 UNI21V
720k 68k 0.0863 0 0 11.6 29.0 40.6 UNI29V
720k 47k 0.0613 0 0 16.3 40.8 57.1 UNI41V
720k 33k 0.0438 0 0 22.8 57.0 79.9 UNI57V
360k 360k 0.5 1.25 -2.5 -0.5 2.5 4.5 BIP2.5V
360k 240k 180k 0.2222 1.111 -5 -0.5 6.3 10.8 BIP5V
720k 240k 180k 0.125 1.25 -10 -2.0 10.0 18.0 BIP10V
720k 68k 68k 0.0451 1.194 -26.5 -4.3 29.0 51.1 BIP25V

The labels in the Name column are used when ordering custom configurations.

U3: The LJTD is generally used with low-voltage channels on the U3-LV or U3-HV.  The nominal input range of a low-voltage channel is 0-2.44 volts, so the input range provided by the LJTD is from the "VIN (OUT=0)" column to a little less than the "VIN (OUT=2.5)" column.  For example, the UNI10V in this case will provide an input range of about 0 to 9.76 volts.  If you set the U3 analog input to the "special" range it takes an input of about 0-3.6 volts, so the input range provided by the LJTD is from the "VIN (OUT=0)" column to the "VIN (OUT=3.5)" column.  For example, the UNI10V in this case will provide an input range of about 0 to 14 volts.

U6/T7: The LJTD is used with the +/-10 or +/-1 volt range on the U6.  With the +/-10 volt range the full 0-3.5 volt output of the LJTD can be measured, but only 3.5/20 = 17.5% of the U6 input range is used.  With the +/-1 volt range, the 0 and 1 volt output columns above apply, and 50% of the U6 input range is used.

UE9: The LJTD is used withe the 0-2.5 or 0-5 volt range on the UE9.  The 0 and 2.5 volt output columns above use 100% of the 0-2.5 volt UE9 input range, or the 0 and 3.5 volt columns use 70% of the 0-5 volt UE9 input range.

 

Specifications:

Parameter Conditions Min Typical Max Units
General
Vs, Supply Voltage (1) 2.8 5 5.5 Volts
Supply Current 1.2 mA
Operating Temperature -40 85 °C
VREF
Output Voltage 2.495 2.5 2.505 Volts
Initial Accuracy ±0.2 %
Maximum Output Current 24 mA
Op-Amp Buffer
Typical Input Voltage Range -0.1 VS - 1.5 Volts
Typical Output Voltage Range Load ≥ 100kΩ 0.001 VS - 0.001 Volts
Input/Output
Slope Error ±0.2 %
Offset Error ±0.2 %
Input Impedance (2) UNI10V 960
Input Bias current (2) VIN = 10V 10 μA

(1) The maximum input voltage to the buffer amplifier is VS-1.5, so for proper operation with signals up to 2.5 volts, VS must be greater than 4.0 volts.

(2) The input impedance and bias current is dominated by the input resistors not the buffer amplifier. The input bias current of the internal buffer amplifier is less than ±200 pA across the voltage range, which is an important number as far as sizing the input resistors to not create excessive offset.

 

Declaration of Conformity

Manufacturers Name: LabJack Corporation
Manufacturers Address: 3232 S Vance St STE 200, Lakewood, CO 80227, USA
Declares that the product
Product Name: LJTick-Divider
Model Number: LJTD
conforms to the following Product Specifications:
EMC Directive: 89/336/EEC
EN 55011 Class A
EN 61326-1: General Requirements

16 comments

Dear all,

I would like to measure voltage between 0 and 15Volt with a very good precision.

Please, can you help me with a configuration.

I have U3 HV, but any suggestions are welcome!

best regards,

Arouna

As a 12-bit device, the U3 provides 4096 counts of resolution.  So the best you could do would be if you built your own voltage divider to convert 0-15V to 0-2.44V.  This would provide a resolution of 15/4096 = 3.7mV.  See the app notes "Noise and Resolution" and "Resolution and Accuracy".

The easiest solution is to use a high-voltage channel and specify 32 as the negative channel.  This puts it in the -10 to +20V special range which has a resolution of about 10mV.  See Section 2.6.1 of the U3 User's Guide.

To improve on this, you need a higher resolution device such as the LabJack U6.

Greetings,

You may have to add Out=10 (for U6 and T7) as ther is Out=2.5 and out=3.5 only.

The reason for the 3.5 volt output column is that the typical output limit for the LJTD is VS-1.5 (from the specs table), so if VS is 5.0 volts then 3.5 volts is the most the LJTD can output.

Hello, I am thinking on buying some of these to interface to a high voltage incremental encoder that runs at 24V. However, I am currently using the FI04 and FIO5 ports of a U3 in HW counter mode since the incoming pulse stream can go as high as 1800000 pulses per second. What is the bandwidth of the op amp that you are using? It is safe to assume that I can still recognize pulses at 2MHz?

The op-amp is the OPA2335, but the limiting factor for bandwidth is the large input resistance with the input capacitance of the amp.  Using 960k and 5pF, I come up with a bandwidth of about 33 kHz.

Excellent! I'll take a look at the opamp datasheet, but it seems like it will work ok. Thank you!

The Feb 11th, 2015, post above was not right.  I just edited it.

How the V5 is connected to this schematics?

I am afraid I do not understand what you are asking.

So you want to build a voltage divider with Slope=1.0 and Offset=0.0?  That would be called a non-inverting buffer.  I don't quite understand if you are modifying an LJTick-Divider (UNI10V or BIP10V?), or just building your own with resistors and an op-amp?  If building your own, see Figure 2.6-3 here in Section 2.6.3.6 of the U3 User's Guide.  In the particular case of Slope=1.0, you would set R2=Inf and R1=0, so you don't need any resistors ... just an op-amp.

Thanks again for your reply. I wanna build a replicate of the LJTD-UNI2V-1M. The details are as follows:

The LJTD-UNI2V-1M has R1=R2=22k (thus R1+R2=44k) and R3=1M.

In that case, should I follow figure 3? And also which opamp should I choose please?

LabJack Support's picture

Figure 3 on this LJTD datasheet has a lot of extra stuff.  Instead I would look at Figure 2.6-3 in Section 2.6.3.6.  You want R1=44k and R2=1M, and that section even suggests an amp (OPA344).

Note that we are now producing the equivalent of the LJTD-UNI2V-1M as a stock item.  They are not posted on the site yet, but I believe we do have stock available.  It is called the LJTick-Resistance (-1k, -10k, -100k, -1M).

Thanks a lot for your kind help. I already have few of those LJTD but want this signal conditioning circuitry on a pcb to save space. Would a normal opamp such as 741 make any diffrence? And also do I need a capacitor across vout to reduce the noise? Thanks.

 

 

There are many details of analog design that are beyond the scope of what we can help with, but I suggest you want a RIRO op-amp with low input bias currents.  As to adding an RC filter, you can do that on the inputs and outputs, but there are many design considerations, pitfalls, and trade-offs.  My quick suggestion would be to add a capacitor in parallel with the 1M resistor (see discussion of C1=100pF on this page).

I exactly followed what you suggested. I considered R1 as 44k and R2 as 1M (Figure 2-5). My Vin is 1v. As op amp is voltage buffer, I should get vout as vin. But my vout is found as 1.88v. I did the simulation on software which gave vout=vin. But when I soldered on PCB and breadboard Vout come as 1.88v. Thanks again.