Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Temperature/Acceleromete TA102 sensor: help needed to measure required sensor data

Status
Not open for further replies.

faiz18

Newbie level 6
Joined
Apr 25, 2017
Messages
12
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
133
Hi all,

I am working on a project that involves using a 1-axis (if I'm not wrong) accelerometer for vibration sensing called TA102 by CTC. This sensor also gives a temperature reading. All this data I send over the network to a gateway. But I am having trouble measuring or making sense of the output at the accelerometer end.

I get the temperature reading but I get a very high value at the accelerometer side. The Sensitivity given for the accelerometer is about 100 mv/g. If I am not wrong, the voltage output at rest should be ~0 mv. But I get a value of around 6.78 VDC. I am little confused as I am not sure if I am measuring the voltage correctly. The circuit I use is given in the pic attached. Would appreciate if some one could help me understand what I should do to get the right value.

Please let me know if you need more information.

Thanks for the help. acc_circuit.JPG
 

Hi,

This is onky a part of the signal flow. Completely missing:
* DC biasing at the ADC side
* protection circuit
* filters
* ADC

Therefore we have to guess. But guessing is not good to focus on problems.
--> show us the complete circuit.

At the output signal there is a series capacitor installed.
It suppresses DC voltage and very low frequency.
The formula for the cutoff frequency is: fc = 1 / ( 2 × Pi x R x C)

If you don't use a "R" to correctly bias the ADC input voltage...
* there will be no correct cut off frequency
* there will be no DC operating point

Klaus
 

Hi Klaus,

Thank you for the reply and sorry for the late response.

Frankly, I don't yet have a complete circuit. I thought I could start first by just measuring the raw voltage values using an oscilloscope or a multi-meter after connecting the circuit as per the image I sent.

I used the resistor and capacitor values that are shown in the circuit and I tried measuring the AC voltage on an oscilloscope but I do not get anything even when I move the sensor around. So I guess I am missing something. I do not have a lot of knowledge on such sensors. So it would help if you could point me in the right direction.

Thanks,
Faiz
 

Hi,

You only get AC voltage at the output when there is some alternating acceleration at the sensor.
How do you accelerate? What are the estimated acceleration values? amplitude, waveform, frequency.

Then do a calculation to get a clue about the output signal you have to expect.

Repeating: You need to connect a R at the output. What value did you choose and what cutoff frequency does this give?

Currently we don't see much effort on your own.

Klaus
 

Hi Klaus,

Let's start with what I have done so far:

The sensor has an accelerometer and a temperature sensor and requires a constant current excitation to function. So we use the CRD for this purpose. For the accelerometer, which I will be using as a vibration sensor, the sensitivity is 100 mV/g. And the frequency response of this sensor is 0.5 to 15000 Hz. So I'll need a very low cutoff frequency in order to get access to this range. With the capacitor which is already part of the circuit, the 22 uF capacitor, and a cutoff frquency of 0.5 Hz (lower range), I get the resistor value of ~14.5 Kohms (using the cutoff frequency formula you provided). So I add in a 15 Kohm resistor at the end of the circuit. But I also get a DC bias voltage i.e. an offset so in order to remove this I'll need a right resistor value. After some trial and error (is there another way to get this value?), I used a 10 ohm resistor to which got rid of the 12 V DC offset and my cutoff frequency is around 700 Hz which is still fine I guess as the frequency response range is quite large (correct me if I'm wrong). So now the circuit is as per the attached picture.IMG_20171222_110258635.jpg

Also I made a mistake earlier of not mounting the sensor onto a plate. So now to sense any change I just hit the plate with a pen so the vibrations lead to a change in voltage which I can see on the oscilloscope. So I have got this far. Now my next task would be to capture this AC signal and convert it to DC so that I can use an ADC and a micro-controller send it over a network. Just wanted to know if I am on the right track.

Thanks for all the help and the push!

Faiz.
 

Hi,

Check both schematics. Your capacitor is in the wrong orientation.
Use 15k.

We can'tknow why you need a DC voltage.
In most cases I'd connect the sensor directely to an ADC. This is the most precise and most flexible way, because you just need some software to process the data.

Klaus
 

Hi Klaus,

Oops. The indication in the second schematic is wrong. I connected it in the right way according to the first schematic. Thanks for pointing that out.

If I use 15 Kohm then I get a bias voltage of 12 V at the o/p. So if I connect this circuit directly to an ADC then won't the 12V be more prominent than the small AC signal?

Faiz
 

Hi,

With a properly connected capacitor there can't be DC at the output.
Either your measurement is wrong, or the capacitor is defective.

Klaus
 

Hi Klaus,

I checked the connections and they seem fine. I'll try with another capacitor just in case. But I think I'm supposed to get he 12 V DC voltage because it says so in the power requirements sheet of the sensor - Attached imagepower_req_TA102.JPG.

Faiz
 

Hi,

Maybe your capacitor connection is wrong.
Show how you did connect it.

Maybe your voltage measurement is at the wrong place.
Show how you connected the voltmeter.

Klaus
 

Hi Klaus,

I checked the connections and they seem fine. I'll try with another capacitor just in case. But I think I'm supposed to get he 12 V DC voltage because it says so in the power requirements sheet of the sensor - Attached imageView attachment 143509.

Faiz

Hi, Have you figure out the correct circuit diagram?
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top