This page outlines the signal range limits in and out of the LJTick-InAmp.
AD623 Diamond Plot Tool
The LJtick-InAmp uses the AD623 instrumentation amplifier. The AD623 Diamond Plot Tool can be used to check if your LJtick-InAmp input and output voltages are valid for normal device operation. The terms used by the tool can be mapped to LJTick-InAmp terms as follows. Our definitions of Vin and Vcm can be found on the main page of the LJTick-InAmp datasheet:
-
"+Vs" = VS (typically 5.0 V)
-
"-Vs" = GND (0 V)
-
"Vref" = 1.25 V
-
“Vcm” = Vcm
-
“Vdiff” = Vin
Signal Range Tables
The following tables outlines the most common voltage ranges used by the LJTick-Inamp. The amplifiers on the LJTick-InAmp have a range of about 0.01 volts to 4.5 volts (VS-0.5).
-
The "Min" column corresponds to the minimum Vin that can be measured. The “Minout” column corresponds to the actual output voltage at the specified minimum Vin. Usually this should be 0.2 V, but sometimes there are other limiting factors that affect the Vout value.
-
The "V1" column corresponds to the Vin that would ideally produce Vout = 2.5 V. If there is some limitation in the circuit that prevents the output from reaching 2.5 V, “V1” instead represents the maximum Vin that produces a valid output. The “V1out” column corresponds to the actual output voltage when Vin=V1.
-
The "V2" column corresponds to the Vin that would ideally produce Vout = 4.5 V. If there is some limitation in the circuit that prevents the output from reaching 4.5 V, “V2” instead represents the maximum Vin that produces a valid output or N/A (indicating the max output voltage is less than 2.5 V). The “V2out” column corresponds to the actual output voltage when Vin = V2.
|
Gain |
Vin (Differential) (Volts) |
Vout (Single Ended) (Volts) |
||||
|
Min |
V1 |
V2 |
Minout |
V1out |
V2out |
|
|
Vcm = 0 V |
||||||
|
1 |
-0.3 |
0.3 |
N/A |
0.95 |
1.55 |
N/A |
|
11 |
-0.09 |
0.0909 |
N/A |
0.26 |
2.25 |
N/A |
|
51 |
-0.0196 |
0.0196 |
N/A |
0.25 |
2.25 |
N/A |
|
201 |
-0.0049 |
0.0049 |
N/A |
0.265 |
2.23 |
N/A |
|
Vcm = 1.25 V |
||||||
|
1 |
-1.05 |
1.25 |
2.8 |
0.2 |
2.5 |
4.05 |
|
11 |
-0.0954 |
0.114 |
0.2954 |
0.2 |
2.5 |
4.5 |
|
51 |
-0.02059 |
0.0245 |
0.0637 |
0.2 |
2.5 |
4.5 |
|
201 |
-0.00522 |
0.006218 |
0.01616 |
0.2 |
2.5 |
4.5 |
|
Vcm = 2.5 V |
||||||
|
1 |
-1.05 |
1.25 |
2 |
0.2 |
2.5 |
3.25 |
|
11 |
-0.0954 |
0.191 |
0.295 |
0.2 |
2.5 |
4.5 |
|
51 |
-0.02059 |
0.0412 |
0.0637 |
0.2 |
2.5 |
4.5 |
|
201 |
-0.00522 |
0.006218 |
0.01616 |
0.2 |
2.5 |
4.5 |
|
Vcm = Vin / 2 |
||||||
|
1 |
-0.15 |
1.25 |
2 |
1.1 |
2.5 |
3.25 |
|
11 |
-0.082 |
0.05 |
N/A |
0.348 |
2.35 |
N/A |
|
51 |
-0.0192 |
0.0098 |
N/A |
0.271 |
2.25 |
N/A |
|
201 |
-0.00494 |
0.005 |
N/A |
0.257 |
2.255 |
N/A |
Signal Range Example
Assume that you have an LJTick-InAmp configured with a gain of x201 and that the Vin signals come from a bridge with 5 volt excitation, so Vcm is 2.5 volts. Using the diamond plot tool or table above, the input signal voltage can range from around -0.00522V to +0.01616V.
As of writing, the AD623 datasheet specifies an output voltage swing of 0.2 V to VS - 0.5 V for RL = 10 kΩ and 0.05 V to VS - 0.15 V for RL = 100 kΩ. The diamond plot tool and table above use the narrower range specifications, but the wider range specifications should be valid since LabJack hardware presents a load resistance that is typically much higher than 100kΩ. In practice, this means that somewhat wider input voltage ranges can be measured than what is estimated using the tooling above, but only when the limiting factor is the output voltage swing.