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LJTick-InAmp Datasheet

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Price: $59.00
LabJack LJTick-InAmp Analog Input Amplifier Accessory Compatible with LabJack USB, Ethernet, WiFi DAQ Devices

 

The LJTick-InAmp (LJTIA) is a signal-conditioning module that provides two instrumentation amplifiers ideal for low-level signals such as bridge circuits (strain gauges) and thermocouples. The LJTIA has 5 gain settings per channel and two selectable output voltage offsets (Voffset). The 4-pin design plugs into the standard AIN/AIN/GND/VS screw-terminal block found on LabJacks such as the U3 and UE9.

The pictures below show the LJTIA plugged into the U3 on the left and plugged into the UE9 on the right.

Figure 1: LJTick-InAmp (LJTIA)

Figure 2: LJTIA With U3

Figure 3: LJTIA With UE9

 

The block of 4 screw-terminals at the left edge of the LJTIA (Figure 1 above) provides a positive and negative input for each differential channel. Towards the LabJack side of the LJTIA is a pair of screw-terminals that provide a ground connection (GND) and a +2.50 volt reference (VREF). The reference is capable of sourcing enough current (see Specifications) to function as the excitation voltage for most common bridge circuits.

In between the blocks of screw-terminals is a 10-position DIP switch used to specify gain and offset.

Table 1. DIP Switch Descriptions

Switch # Name Description
1 BxR32 Custom gain determined by R32 Applies to channel B only. All off equals a gain of 1.
2 Bx11 Gain of 11
3 Bx52 Gain of 51
4 Bx201 Gain of 201
5 0.4V Output offset of +0.4 volts. Voffset applies to both channels. Switch # 5 or 6 should always be on, but not both.
6 1.25V Output offset of +1.25 volts.
7 AxR17 Custom gain determined by R17 Applies to channel A only. All off equals a gain of 1.
8 Ax11 Gain of 11
9 Ax51 Gain of 51
10 Ax201 Gain of 201

Each channel has a switch (numbers 1 & 7) that has been left without factory-installed gain resistors:  R17 for channel A and R32 for channel B.  Resistors can be installed by the end-user to provide custom gains according to G=1+(100k/R). For example, a resistance of 100 ohms would provide the maximum allowable gain of 1001.  Also, multiple switches can be closed at the same time to get a few other gains (x61, x211, x251, and x261), as the gain settings resistors (10k, 2k, and 500) wind up in parallel. The packages for resistors R17 & R32 are 0805, while all other resistors and capacitors are 0603. The tolerance of the factory installed resistors is 0.1% & 25 ppm/degC, so consider the RG20P series from digikey.com (100ohm = RG20P100BCT).

Extending from the back of the LJTick-InAmp are four pins. The first two pins provide +5 volt power and ground from the LabJack. The other two pins are the instrumentation amplifier outputs and connect to analog inputs on the LabJack. The four pins plug directly into the 5.0 mm spaced screw-terminals on the LabJack U3, UE9, or other future devices as shown in Figure 4.

Figure 4: LJTick-InAmp lined up to UE9

 

Each channel on the LJTIA has an AD623 instrumentation amplifier (in-amp) from Analog Devices. The allowable signal range (Vin) is determined by a combination of Gain, Voffset, Vcm, and Vout. See the Signal Range Tables in Appendix A.

Voffset: This is an offset voltage added to the in-amp output. If DIP switch #5 is on, the offset is +0.4 volts, and if DIP switch #6 is on, the offset is +1.25 volts. The same offset applies to both channels of the LJTick-InAmp. One offset must always be selected (0 volts is not an option), but both offsets should never be enabled at the same time. The +0.4 volt offset is generally used with signals that are mostly unipolar, while the +1.25 volt offset is generally used with bipolar signals.

Vcm: This is the common mode voltage of the differential inputs. For an in-amp, that is defined as the average of the common mode voltage of each input. For instance, if the negative input is grounded, and single-ended signal is connected to the positive input, Vcm is equal to Vin/2. Another common situation is when using a wheatstone bridge where VREF=2.5 is providing the excitation. In this case, each input is at about 1.25 volts compared to ground, and thus Vcm is about 1.25 volts.

Vin: This is the voltage difference between IN+ and IN-. In the following Signal Range Tables, the “Low” column is the minimum Vin where Vout is 10 mV or higher, the “High 2.5V” column is the maximum Vin where Vout is 2.5 volts or less, and the “High 4.5V” column is the maximum Vin where Vout is 4.5 volts or less.

Vout: This is the single-ended (referred to ground) voltage output from the in-amp. Because of the power supply to the in-amp, the full output swing is about 0.01 volts to 4.5 volts. The “Low” and “High” columns in the Signal Range Tables give the output at the respective Vin.

 

Specifications

Parameter Conditions Min Typical Max Units
General          
Supply Voltage   3.6 5 5.5 volts
Supply Current No Loads   1.5   mA
Operating Temperature    -40   85 °C
Signal Specs          
Gain Accuracy (1)   0.35 1.2 %
Offset Accuracy (1) G = 1    0.5 1.2  %
  G = 11    0.5 1.2  %
  G = 51    2.5 4.0   %
  G = 201    10 15.0   %
Input Bias Current (2)     17   nA
 Input Impedance      2  
Each Input vs. GND (3) Normal Operation     -0.3 to +5.3 volts
Each Input vs. GND (3) No Damage     -10 to +15 volts
Typical Output Range Load ≥ 10 kΩ 0.01   VS - 0.5  
-3 dB Bandwidth x1   18   kHz
  x11   18   kHz
  x51   18   kHz
  x201   10   kHz
Vref          
Output Voltage   2.495 2.50 2.505 volts
Initial Accuracy     0.2   %
Current Output (4) For rated V accuracy 0   25 mA

(1) The max accuracy specs are the tested device limits and are expected to be met whether device is warmed up or not.  Typical specs are what is normally seen with a warmed up device at room temperature. Gain and offset are very stable at a stable temperature, so a user-calibration can achieve accuracy much better than the specs listed here.
(2) The current in/out of the input terminals is nanoamps from -0.3 to +5.3 volts.  Beyond that range it increases up to 10mA at -10 or +15 volts.
(3) This is the limit of the voltage on any input terminal versus ground.  See Appendix A for actual limits in different situations.
(4) Higher currents will not cause damage, but the reference voltage will start to sag. The reference output can handle a continuous short-circuit to ground and has a short-circuit current of about 45 mA typically.

Dimensions

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-InAmp
Model Number: LJTIA
conforms to the following Product Specifications:
EMC Directive: 89/336/EEC
EN 55011 Class A
EN 61326-1: General Requirements

18 comments

Is it possible to use the LJTick-InAmp with the LabJack U12? I'm guessing the output prongs won't fit directly into the U12, but a little solder and wire can fix that. If it is possible, can you give some advice on the best way to do it? Thanks a lot. -Seth

Yes, you can use wires to connect an LJTIA to a U12.  This forum topic has good info to get started:

http://forums.labjack.com/index.php?showtopic=2390

 

If you have a +-10V differential input you are trying to measure with a UE9, and you are unsure if you can connect the commons, can you connect a tickinamp with a gain of 1 to the back of a bipolar tick divider and plug it into a UE9?  

So your signal has a positive, negative, and common, and you are not sure if you can connect the negative and common both to GND on the UE9?

You could do what you describe, but once you use the LJTick-Divider you would be better off to just connect both signals to the UE9 analog inputs rather than using an LJTick-InAmp in between.  Take the 2 single-ended readings and subtract in software.

Note that there must be some sort of reference to UE9 ground.  See the Differential AIN App Note.

Is it possible to use the LJTick-InAmp with the LabJack U6, and what is the best solution for load cell and similar sensors, where is the base U6?

Thanks in advance.

Forum topic 4376 has general information about bridge circuits.  The U6 or U6-Pro by itself is the best for bridge circuits.  You can use the LJTIA with the U6, but the U6 has a similar amp built-in so the LJTIA is generally not needed.  A few reasons you might use the LJTIA with the U6:

 

  • The Vref source on the LJTIA is useful for bridge excitation, although using the DACs on the U6 works great.
  • Normally the differential bridge signal connects to 2 analog inputs on the U6, but the LJTIA converts differential to single-ended, thus you only need 1 U6 analog input per bridge.  Keep in mind that the Mux80 is an inexpensive way to add lots of analog inputs to the U6.
  • When you use higher gain on the U6, more settling time is needed when switching from 1 channel to the next (see Section 3 of the U6 User's Guide).  If you use the LJTIA to provide external amplification for each channel, then you can use lower gain in the U6 and scan faster.

 

Hi,

I am trying to measure current(0.6A) using a sense resistor of 1ohm,3W. I have a voltage drop of .006v at the sense resistor. Now I am trying to amplify it using LJTickInAmp setting a gain of 201 and an offset of 0.4v. So at the output,I should get .006*201+.4=1.61v. But I am not getting it. Well, of course there is some amplified signal at the output(at least greater than the offset .4v). But this is much lower than it should be. What might be the problem? Well,what's the minimum differential input that LJTickInAmp can detect? Is .006v enough?

Thanks.

Describe all connections to the LabJack and LJTIA so we can help troubleshoot.

See the Differential Analog Inputs app note.  Is the shunt installed on the low-side of you load such that one side of the shunt is at ground?  Or if the shunt is high-side, what is the voltage on each side of the shunt compared to ground?

Refer to the signal range tables in Appendix A of the LJTIA datasheet, or use the calculator linked at the top of that page.  If you have a low-side shunt, then your common-mode voltage is Vin/2, so with Voffset=0.4 and Gain=x201 the Vin range of the LJTIA is -1.9mV to +5.9mV.

Ok problem solved. It seems that I did not connect the grounds of dc supply voltage and labjack(i,e,Ljtick). Now it's working. However, the output should be constant 0.58 Amps(I have converted the voltage signal to current inside the program). But it's swinging too much from 0.2 Amps - 0.6 Amps. What can I do to make the output stable?

The shunt resistor is connected to the low side of the load. So the positive side of the shunt goes to INA+ and the ground of the shunt goes to INA-. And the shunt ground(i,e, dc supply ground) is connected with the ljtick ground(i,e,labjack ground) through a 10k resistor.

So the reading from the LJTIA is varying from 2-6 mV, when you expect a constant 6 mV.  You might have to connect a scope from INA+ to INA- to see if the signal is actually varying.  Also look at INA+ to GND and INA- to GND to see if you see anything unusual there.  Does it make a difference if you drop the 10k series resistor to 100 ohms or even just a jumper wire (0 ohms)?

If you turn off the supply to the load, or better yet disconnect the wire, so that you know current through the shunt is 0 amps, do you get a constant 0 mV from the shunt?

Also, try removing your signal and jumper both LJTIA inputs to GND.  Then you can see how the LJTIA reads when the input voltage is at known steady 0.0.

Note that Hall-Effect sensors are generally an easier way to measure current as the signal is isolated from the load.  Consider the SCD03PUN which gives you about 767 mV/A.

Dear,

I’m working on a retrofit of a Tensile testing machine, which consists of replacing load-cells, and installing an acquisition system with PC software that calculates all necessary data and charts a diagram.

After a series of successful applications, I tried to achieve the same results with your products. But I ran into some difficulties. Currently, I am using a Laumas load-cell CL100000 kg (2mV/V, resistance 700Ohm, combined error ±0.05%) and LabJack U6 - Pro with LJTick-InAmp to amplify the signal. The setup is as follows:

 

  • ·         U6 – Pro AIN range is set to ±1V
  • ·         Resolution index set to 9
  • ·         LJTick-InAmp set to amplify x51 and offset 0.4V
  • ·         Load-cell supply is coming from DAC output (4.5V)

 

According to Appendix B - Noise and Resolution Tables for resolution index 9 (effective resolution should be 2.6μV) I made the following calculation:

Signal from the load-cell for full range is 9 mV, after amplification (x51) signal on AIN0 should be around 459 mV. Which means that 1N should be around 0.459μV, and that I could get the resolution of at least 10 N. That would be enough to satisfy my needs. But, in practice I can’t even remotely achieve that resolution. My signal has fluctuations of a few hundred μV (300-400 N).

Am I making some kind of a systemic error? Do you have any idea of what I could be doing wrong, how to fix it and achieve the resolution declared in the datasheet?

Many thanks in advance,

 

 

One major noise source missing from your calculation is the noise of the LJTick-InAmp.  For example, if you look at the AD623 datasheet it states an input voltage noise of 3uV for 0.1Hz to 10Hz, which at G=x51 would be 153uV at the output.  The bandwidth of the LJTIA is 18khz, so that noise source will be bigger in our case, and that is just one noise source.  I did a quick check and see a basic output noise level of about +/-900uV with the LJTIA at G=x51, but you will generally see lower values as the U6-Pro will suppress some or much of this noise.

To check the noise level of your U6-Pro jumper AIN0 to GND.  To check the noise level of the U6-Pro with LJTIA, jumper INA+ to INA- to GND.  When I do this with LJTIA Gain=x51, U6-Pro Range=+/-1V, and U6-Pro ResIndex=9, I see a basic noise level of about +/-100uV.  At ResIndex=12 I see about +/-30uV.

In general, the reason to use the LJTick-InAmp with the U6-Pro is when you need to collect data at higher data rates.  At lower data rates the best noise/resolution performance is usually achieved by connecting the signal directly to the U6-Pro and using maximum ResolutionIndex and minimum Range.  How fast do you need to scan how many channels?

Required scan speed goes up to 100 Hz, two channels for bridge (load cell),  plus a one channel for potentiometer (signal 0 - 5 V) and rotary encoder.

You are expecting a 0-9mV signal, and for 10kg resolution with a 100000kg load cell you need 1/10000 resolution, so 0.9uV.

At 100 Hz, you might be able to use ResIndex=9 on your U6-Pro, but it will be close.  To see how close the U6 can get to your desired noise performance, jumper AIN1 to AIN0 to GND, and then take differential readings of AIN0-AIN1 with ResIndex=9 and using the +/-0.01V range.

To improve on that, you will have to build or find a special low noise amplifier that maintains a 10000:1 or better signal to noise ratio.  I'll try a filter on the LJTIA output to see if that helps much.  What is the desired bandwidth for your signal?

Because our sampling rate is below 100 Hz, suppose that, bandwidth should be up to 50 Hz.

LJTIA with Gain=x51:  Your 0-9mV bridge output will provide a 0.4-0.859V signal for the U6, so a span of about 460000uV.  The LJTIA has a 110 ohm series resistor on its output, so you just need to add a cap from AIN0 to GND to make a filter.  I had a 47uF ceramic cap handy to test, so that makes a low-pass filter with a -3dB point at 30Hz.  With the U6-Pro set to Range=+/-1V and ResIndex=9, the peak-to-peak noise I measure with LJTIA inputs grounded is ~200uV without the cap and ~100uV with the cap.  460000/100 is about 4600:1, compared to your desired 10000:1 signal to noise ratio.

U6 direct:  I tested by simply jumpering AIN1 to AIN0 to GND and taking differential measurements of AIN0-AIN1.  With Range=+/-0.01V and ResIndex=9, the peak-to-peak noise I see on my U6-Pro is 2.4uV.  Your signal in this case has a span of 9000uV, so we are getting 9000/2.4 => 3750:1.

EI-1040:  I did a test with the EI-1040 amp we sell.  You would set this to Gain=x1000 which would give you a signal span of 9000000uV.  I connected the EI-1040 to my U6-Pro and jumpered its inputs to GND.  With Range=+/-10V and ResIndex=9, the peak-to-peak noise I see on my U6-Pro is ~1400uV, dropping to ~700uV with a 100ohm-47uF filter between the EI-1040 and U6.  9000000/700 => 12857:1, so this setup exceeds your desired 10000:1 ratio.

So in this case the EI-1040 works best.  Probably because it can amplify your signal to 0-9 volts which works well in this case.

This is all still with ideal signals.  There might be more noise added by your bridge, and of particular concern is that any bridge excitation noise will appear proportionately in the bridge output signal, so a 4.5 volt excitation source will need to have 4.5/10000 => 450 uV of noise or less.  That seems reasonable for DAC0, especially using ResIndex=9.

Also, about special low noise amplifier, can you help with information where and which type of amplifier I can buy?

We don't have any specific amps we have tested, or have available to test, but here are some possibilities:

http://www.omega.com/pptst/DRC-4710_4720.html
http://www.omega.com/pptst/CCT.html
http://www.omega.com/pptst/DRF-LC.html
http://www.analog.com/en/content/cu_available_5b_series_modules/fca.html

The best option would be the last link.  5B modules are the lowest cost and run off a 5V power supply which you can provide from the U6.  Consider the 5B30, 5B38, or 5B40, and then you can use a 5B03 or 5B04 to provide screw-terminals.

To check the noise output of an amp, connect it to the U6 and configure as it will be used, but short the amp inputs to ground.  Then take U6 measurements to see what the noise level is.  To best see the noise output of the amp you want to use ResolutionIndex=1 so that the U6 is not attenuating any noise (later you can also check the noise level at ResolutionIndex=9 to see what you might be able to get in your particular application).  The output amp output signal for this test should be near 0.0, so you can use any range on the U6.  With ResIndex=1, the noise-free level of the U6 at each range from Appendix B is 1300uV, 220uV, 76uV, and 24uV.  To see the noise of the amp it will have to be greater than the noise of the U6.