Just bought a HPS140i and test signal is not square

Instruments HPS140 Handheld Pocket Oscilloscope
1

Hi everyone,

I have just bought a HPS140i from Maplin, first of all the box says that the test probe should be included with the 140i but they made me buy one separately is this right?

Secondly I assumed it would have a PC output but doesn’t look like it does… (my fault I guess for not checking)

Thirdly, from looking at the introduction videos on youtube it looks like the test signal from the back should be a perfect square wave but I get some kind of misshaped square which doesn’t look at all like a square wave.

Sorry for the newbie questions but I am new to oscilloscopes, I only need it to measure the inductance of a coil I assume the HPS140i will be good enough for this?

2

Hi,

There are 2 different models.
HPS140 (no probe) HPS140I (with probe)

It’s not stated anywhere that there is a PC I/F.

The test signal in the back is to set up the X10 portion of the probe.
Set the probe to X10
Set the scope to X10
Set the voltage per division to 1V
Set the time per division to 0.1 ms
Select AC input

Adjust the trimmer on the probe until the square wave is flat.

Just so you know I got these instruction from the HPS50 users manual.
However I think they are the same for the HPS140 / I

I hope this helps.

3

[quote=“Wrong Way”]Hi,

There are 2 different models.
HPS140 (no probe) HPS140I (with probe)

It’s not stated anywhere that there is a PC I/F.

The test signal in the back is to set up the X10 portion of the probe.
Set the probe to X10
Set the scope to X10
Set the voltage per division to 1V
Set the time per division to 0.1 ms
Select AC input

Adjust the trimmer on the probe until the square wave is flat.

Just so you know I got these instruction from the HPS50 users manual.
However I think they are the same for the HPS140 / I

I hope this helps.[/quote]

Thanks for your advice
Yes mine is the 140i and says probe included in small writing on the box (although I didn’t see this before I bought it)

I know it isn’t stated anywhere it was my mistake I just wanted to find out if there was any way I could get the data to a PC or not but I guess not

I will try that setup properly later but from an initial attempt I just got a flat line so I will have a play.

4

Please confirm the test signal from the back so I know I’m reading/using the HPS140 correctly …and to determine whether dementia and alzheimer’s have kicked in. Last time I used an oscilloscope was 30+years ago so my brain’s SNR is maybe -3dB at best.

I adjusted the probe capacitor in 10x mode with little plastic screwdriver to get a nice wave with sharp 90-degree corners.

75% duty cycle square wave (0.3 msec high / 0.1 msec low)
0.4 msec cycle = 2.5kHz frequency = 1 cycle/0.0004 seconds

My Volts peak-to-peak varies considerably by moving the X-position around, from 3.405 Vpp to 7.836 Vpp when viewing a trace stored in memory. How is this possible?
Am I doing something wrong? Vmin = -2.52 V, Vdc = 0.068V (it should be higher given the 75% duty cycle), and 1.396Vac.

Is the Vac accurate for every waveform, i.e. true RMS?

Looking at the “freq mark” my little Velleman is displaying 862.0Hz. Which doesn’t make sense.

The Fourier dude says I should have the fundamental frequency of the pulse train @ 2.5 kHz plus harmonics 5 kHz, 7.5 kHz, 10 kHz, 12.5 kHz, 15 kHz, 17.5 kHz, 20 kHz. If the waveform were symmetric I wouldn’t hear any even numbered harmonics, right? All of these are way more biggerer than 862 Hz.

I need to be able to trust the readings or at least understand where it’ll fail me and not rely on it while I’m up in a ceiling on a ladder over a french fryer with hot grease cooking onion rings below. My brain’s SNR drops to -110dB in such situations. I need to focus on avoiding to succumbing to 3rd degree burns and not performing mental math.

My parents wouldn’t let me do “math” in school because it’s a 4-letter word. Any assistance, even if half cocked and half vast, may have a modicum of utility. I’ll even appreciate it, so thank you ahead of time --for your time, …just in case I don’t.

Signal analysis should be intuitively obvious to the most casual observer and comprehension readily verifiable.

Fundamental Flaws = Major Malfunctions

5

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