If you have questions about CN0301, please post them below.
I have two questions about CN0301_Evaluation_Software.
When I choose the units of Inches or Millimeters, the change in value on channel 2 is the same. Why? The units we choose are different, but the change in value is the same. For example, they all go from 0.0156 to 0.0176.
When I change the maximum stroke range of the LVDT, the values on channel 2 are quite different. For example, when I set 0.20 inches, the value on channel 2 go from 0.0030 to 0.0036. When I set 1.00 inches, the value on channel 2 go from 0.0156 to 0.0176. What the relationship?When you do an experiment, how do you set the maximum stroke range of the LVDT?
We have checked and validated the results you were getting for both questions that wrote.
for question 1: as per reviewing the source code, the conversion unit was not implemented and therefore needs to be added by editing the software where the link was provided by Brandon.
for question 2: we were able to encounter same issue when the LVDT sensor was not properly connected to the terminal. once the connection was fixed properly, the reading correctly corresponds again to the max stroke provided. kindly make sure that the sensor was properly connected to theboards terminal input connector.
Sorry,I was busy with something else the day before, and I didn't reply to you until today.
I have made some experience with the updated software. There is no problem switching between inches and millimeters. For example, when I choose the units of Inches, the value on channel 2 is -0.0565, and when I choose the units of Millimeters, the value on channel 2 is -1.4335. There is no problem.
But,when I change the maximum stroke range of the LVDT from 0.20 inches to 1.00 inches, the value on channel 2 also change from -0.0565 to -0.2825. They both have a five-fold change in relationship. Is this right?
I have anthor question. When I connect LVDT and do nothing, the waveform is shown as follows.
You can see that the error is quite large. Where do you think this error comes from?
I did not use the E-100 ECONOMY SERIES LVDT. I used the sensor of my own and have tested the input and output signals of the sensor. There is no problem.
thanks for confirming that no further issue found for the conversion function of length displacement.
the initial value under the max stroke relates to the specs of the included E-100 LVDT for this reference design and its specs can be read from this link:
as what you mentioned above, you were using a different LVDT. you, therefore, need to change some of the resistor component values in the reference design that contributes in setting the right scale measurement of its displacement being displayed in the GUI. kindly refer to page 6 from the datasheet of AD698(https://www.analog.com/media/en/technical-documentation/data-sheets/ad698.pdf) for your reference.
and for the error that you are seeing from its acquired data when the LVDT is at its static state which gives you a .00005in as its noise is still in its acceptable range of noise value.
Thank you for your help. I have the last two questions.
How can I change the values of the resistor component in the reference design? The board I bought has been integrated. Do I need to order a new one?
You said "0.00005inch noise is in its acceptable range",I want to know can this set of equipment make ultra-precise measurements? 0.00005inch=1.27micron. I want to use this equipment to measure surface roughness. My LVDT sensor has a resolution of 0.1 micron. Generally, the roughness of precision devices needs to be up to 0.1 micron. Can this LVDT processing equipment meet my requirements?
First of all, you do not need to order a new board; but since you are using a different LVDT sensor, you will have to replace the AD698 gain resistor and offset resistor with different values.
The resistors used to set the gain are R9 and R10 (for channels 1 and 2 respectively). The value of these resistors is calculated using the equation below (from AD698 datasheet, page 7):
Where VOUT is the desired AD698 full-scale output voltage (5 V for CN0301), S is the sensitivity of the LVDT sensor, d is the stroke span and 500 µA is the AD698 reference current.
You can check the spec sheet of your LVDT sensor for its sensitivity. If it's not there, page 10 of the AD698 datasheet shows the procedure to calculate it.
It should be noted that using the E100 LVDT stroke span of 0.2 inch and sensitivity of 2.4 V/V/inch with the above equation gives you RG = 21 kΩ, the value of the resistors we installed for R9 and R10.
Next are the resistors used to set the output offset are R14 and R15 (for channels 1 and 2 respectively). The value of these resistors is calculated using the equation below (from AD698 datasheet, page 7):
Where RG is the gain resistance and VOS is the desired output offset (+2.5 V for CN0301).
Regarding your second question, CN0301 uses the AD7992 which has a 12-bit resolution. This means that with the AD698 output effectively ranging from 0 to 5 V, the input voltage represented by 1 LSB will be:
You can then use the AD698 transfer function to check if CN0301 will be able to meet their requirement (from AD698 datasheet, page 7):
Where VOUT is the AD698 output voltage (1 LSB in this case), S is the LVDT sensor sensitivity, d is the core displacement, 500 µA is the AD698 reference current and RG is the gain resistance.
For example, using the gain resistance of 21 kΩ and the E100 LVDT:
Thus, the displacement represented by 1 LSB is:
Clearly, the default configuration of the CN0301 will not meet your ultra-precise requirement of 0.1 µm resolution but an LVDT sensor with better resolution and sensitivity than the E100 should yield a better result.
Please refer to the CN0301 user guide and AD698 data sheet for more details on this.
Thank you for your help all the time.