Probes: x1 or x10 modus
First the specs you'll get using the probes at 1X/10X with SmartScope (they are not exact, just approximate reference values):
| x1 | x10 | |
|---|---|---|
| Impedance | 1 MΩ // 100pF | 10 MΩ // 20pF |
| Bandwidth | 6 MHz | 30 MHz |
| Max. Voltage Range | ±30 V | ±300 V |
| Max. Amplitude | 40Vpp | 400Vpp |
| Voltage Resolution (V/AdcUnit) | 2 mV | 20 mV |
Let's talk about all that...
Impedance: This will be the load you'll apply to the point under test. When you are probing a node you are adding a 1/10MΩ resistor to ground in that point and a parallel capacitor of 100/20pF to ground too. That means that a 10X probe will be better because it'll have less impact on the actual signal in the circuit.
Bandwidth: To put it simply, the bandwidth tells you from what frequency up the signals will be 'smoothed'. If you are working with sine waves you'll only get attenuation, but for square or any complex signal they need to be 1/10 of the bandwidth or slower, otherwise you'll see distorted waveforms. So what this means? At 1X you'll be limited to 600Khz square signals but at 10X you can go up to 3Mhz square signals without significant deformation. So once again a 10X probe will be better. The probe is actually 60Mhz but the scope has 30Mhz bandwidth (You actually always want your probe to be of higher bandwidth that the scope otherwise you'll get double attenuation).
By the way, all this does not mean that you cannot see signals faster than 3Mhz, you can, actually you can see signals all the way to 50Mhz (half of the sampling frequency), but after 3Mhz you'll start to notice the loss of higher frequency components, meaning edges will not look as sharp as they actually are.Around 20Mhz or so you'll see everything like a sine wave, and after that you'll get into aliasing problems reaching the limits of the sampling rate.
Max. Voltage Range: Since you have 10x attenuation you'll have 10x more range. So 10x probe is better again. Actually, it is a bit more complex, because the probe could be damaged if the voltage and the frequency are both high (and it could also damage the scope). Without entering in details this is a simple table of the safe voltage ranges with the probe in 10x:
| Frequency | Voltage Range |
|---|---|
| 0 - 20 kHz | ±200 V / 120 VAC |
| 20 kHz - 200 kHz | ±100 V / 60 VAC |
| 200 kHz - 50 MHz | ±25 V / 16 VAC |
Max. Voltage Resolution: This is the minimal voltage difference that the ADC of the scope can measure (with the volts/div in the lowest ranges of course). Here 1x probe is better because due to the probe attenuation you'll have 1/10 of the resolution. But of course this will only be true in the lowest ranges, once you get to 500mv/div you'll have the same resolution using 1x or 10X probe.
So, long story short, a 10x probe will be better in all cases except two:
- When you want to measure small signals (under 2Vpp) with more resolution than 20mV.
- When you are measuring signals of 1Mhz or lower and you want to filter out high frequency noise (over 6Mhz).