# Calibrating your probe after capturing waveform

Michael Technician California Posted   Latest   Edited

I've been encountering a lot of shared wave forms on here and from others not having calibrated there probes and the result is a psi measurement only shown in volts.

How can i convert the voltage to a psi unit using math channels for the WPS500?

Here is the conversion formula.

Scaling

Range 1

1 V/100 psi (6.89 bar)

Range 2

1 V/10 psi (0.689 bar)

Range 3

1 V/1 psi (0.0689 bar)

Conversion factors The SI unit of pressure and vacuum is the pascal, symbol Pa. These are some other units in common use: 1 bar 100 000 Pa 1 psi (pound per square inch) ≈ 6 895 Pa 1 inHg (inch of mercury) ≈ 3 386 Pa 1 inH2O (inch of water) ≈ 250 Pa 1 mmH2O (millimeter of water) ≈ 10 Pa

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Dmitriy Analyst
Ontario
Dmitriy

Michael, I do not recall a PsData file posted here that would have Volts instead of Psi or Bar. Could you provide a link to an example?

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Michael Technician
California
Michael

Here's an example

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Dmitriy Analyst
Ontario
Dmitriy

I opened it in Picoscope Automotive and it shows PSIs... What does it show for you? diag​.​net/file/f3dk378d6… ​

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Michael Technician
California
Michael

Where did that psi math channel come from? I dont see that anywhere

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Dmitriy Analyst
Ontario
Dmitriy

It is not exactly a math channel. It is Channel B with "WPS500X range 1" probe selected in its settings. Makes it automatically show corresponding pressure values.

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Michael Technician
California
Michael

Im sorry let me be more specific! Im talking about channel A which shows voltage and is an intake vacuum pulse waveform!

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Dmitriy Analyst
Ontario
Dmitriy

Ahh, that's what you are after! Well, it's a signal from a pressure pulse sensor, not pressure sensor. The sensor outputs voltage that is approximately proportional to the rate of change in pressure. Some information about the actual pressure is, unfortunately, lost in this process. If an analogy helps, pressure pulse to pressure is what speed of a car is to distance travelled. Related, but…

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Michael Technician
California
Michael

So if it is a WPS500 but the probe wasn't calibrated before testing, there is no way to convert the voltage to a psi math channel that post-test? I tried A*10*2.03 but no luck on the accuracy

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Dmitriy Analyst
Ontario
Dmitriy

Please provide a PsData file that has signal (confirmed to come) from WPS500 shown as voltage, I will explain how to transform it.

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Jj Technician
Massachusetts
Jj

I'm pretty sure channel A in that capture isn't from a WPS500. I don't think the WPS does pressure pulse. What you're looking at is more likely from a First Look Sensor or other pulse sensor. They don't show actual pressure, but pressure changes. Its a visual representation of, say, pressure pulses in the exhaust or vacuum pulses in the intake. They measure pressure changes, but not actual…

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Dmitriy Analyst
Ontario
Dmitriy

Jj, I’d like to add that while typically WPS500 measures the actual pressure, it has a special “zoom mode” in which its output mimics pressure pulse sensors. More on this here: aeswave​.​answerbase​.​com/978568/Does-th…

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Jj Technician
Massachusetts
Jj

Good to know. If a capture were to have both a pressure signal and a pulse signal there would need to be two WPS500s in use? One set to range 1 and one set to zoom?

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Dmitriy Analyst
Ontario
Dmitriy

You mean to use a Tee fitting and plumb two WPS500 into the same pressure source? It would work, but might not be necessary as one could use a math channel in Picoscope to calculate pressure pulse values from the actual pressure values. I hope to write a post on the subject if my bounty gets completed: diag​.​net/msg/m2uwl1rlg9…

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