ADS1115 ceramic capacitor: decoupling / noise removal?

[WBr]

I have a question.

When using a differential sensor like the MPX53DP and an ADS1115, one mentioned to me that two ceramic capacitors:

104 (0.1uF)
106 (10uF)

Are used for bridging pin A0 and pin A1 to reduce noise.

Two data wires from the differential sensor are connected to A0 and A1.

Does this make sense?

[WBr]

Internet doesn’t explain too much on this situation..

[Colin]

Have you posted this on the correct forum? It doesn't appear to be related to node-red particularly.

[WBr]

Well, the readings are done with nodes hahaha and the noise was also visible in node red. But if you think that i must check other forums.. I always felt the knowledge is quite broad on this forum

[awneil]

@WBr

one mentioned to me that two ceramic capacitors ...

Who mentioned that? Did you ask them to explain themselves?

Can you post a link - so that we can see it in context?

@WBr

if you think that i must check other forums

Yes, the question would be more appropriate elsewhere.
I would suggest starting with the manufacturer's support sites for those chips - they will have datasheets, app notes, etc on using their parts...

[WBr]

@awneil

Did you ask them to explain themselves?

Cant!

I just posted this on an other forum, will update if i have an answer

[davidz]

No this is incorrect in general if you have two different AC input sources at A0 and A1.
The capacitors will create larger crosstalk between these two channels A0 and A1 (assuming that A0 and A1 are both analog inputs).

But if you are measuring DC voltage levels, then this is correct.

[iiot2k]

The MPX53DP has a output voltage +/- 60mV.
Also is the ad1115 input range is +/- 256mV with input mux A0-A1.
I recommend using a bipolar signal amplifier with shortes connection to MPX53DP.
Remove the input capacitors.
These put a capacitative load on the adc input.
Use shielded cable and connect the shield only to one point on ground.
Otherwise, eddy currents will occur.
Connect unused adc inputs to ground.

[WBr]

@davidz

assuming that A0 and A1 are both analog inputs)

Yes, they are

@davidz

But if you are measuring DC voltage levels, then this is correct.

I am indeed reading the two DC values coming from the MPX that needs to be converted to digital

[WBr]

@iiot2k

Remove the input capacitors.

The elco?

Or the two at A0 and A1? (the 106 and 104 ceramics)

[davidz]

OK if you are reading static voltage values, these two capacitor will help reduce the input noise.

If you are using MPX53DP to measure dynamic pressures (varying voltage outputs), then these two capacitors should be removed (They will slow down the response).

[WBr]

@davidz

OK if you are reading static voltage values

The voltage will change according to the measurement that the MPX53DP makes. When the pressure changes, so will the voltage that enters A0 and A1 (as the MPX has two wires, one for each pressure sensor)

So this isn't static (but maybe I misunderstand what you mean)

[davidz]

Does the pressure change quickly, or slowly? The capacitors will remove high frequency components including quick pressure change and noises.
You will get slower, but smoother output (less noisy too).
Dynamic pressure measurement wants to capture the quick changes, so the capacitors won't work.
But for slow pressure change, the capacitors are good.

What is your sample rate at ADS1115?

[WBr]

@davidz

Does the pressure change quickly, or slowly?

Define slow haha

@davidz

What is your sample rate at ADS1115?

I need 1 measurement per second if that is what you mean

[davidz]

1 measurement / second is slow. The capacitors will help reduce noises and variations.

[WBr]

But that is what I need. Not sure if that is what the ADS1115 internally does (as i just hook it up to tasmota and send the data via MQTT to node-red. Or doesn't it make a difference

[awneil]

@WBr

Define slow haha

How quickly can your measurement change?

Can it change by 50% in a second? or would it take an hour? or what?

It's important to understand the nature of what you're measuring to get good results...

[WBr]

@awneil

It's important to understand the nature of what you're measuring to get good results...

Let me keep it simple by saying, heat up liquid in a boiler with a limited opening for pressure release but sufficient enough to keep the system at atmospheric pressure - under correct conditions - .

And this is what the MPX53DP is for! Checking if all is right or when pressure builds up. The pressure must be sort-of equal between 2 points (that's why i use a differential sensor) this pressure and its difference will be checked against current atmospheric pressure (BME280)

[hotNipi]

If sensor board fails the boiler blows up or is there some kind of reliable safety measure included into system?

[WBr]

No risk of explosion haha. Just a messy sticky floor