Automotive Oscilloscope Comparative Specifications |
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PicoScope 4225A
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PicoScope 4425A
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Picoscope 4823
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Oscilloscope Vertical |
Channels
Channels are the number of inputs or the number of waveforms that can be shown simultaneously. |
2 |
4 |
8 |
Bandwidth
Bandwidth is the frequency an oscilloscope can display. High frequencies are the signal's detail. As the signal frequency increases near the bandwidth limit, the scope cannot amplify the signal and the wave gets smaller on the display. The bandwidth is usually specified as the frequency at which the scope displays the signal at half of its true size. If you want to see all the detail in a signal accurately, there is a rule of thumb: the bandwidth needs to be five times the frequency of the signal you are trying to see! Many competing automotive oscilloscopes only have a bandwidth of between 200kHz and 2MHz and therefore you can only see signals between 40kHz and 400kHz reliably, compared to the PicoScope which can see 4MHz. |
20MHz (10MHz on ±50mV Range) |
20MHz (10MHz on ±10mV and ±20mV Ranges) |
Vertical Resolution
The vertical resolution is the number of bits determine the number of discrete values (dots) that can be displayed vertically on your graph. An 8 bit scope can only display 256 dots resulting in a grainy display. A 12 bit scope can display 4096 dots resulting in a far smoother display and greater accuracy. The extra 4 bits means that for every dot displayed by an 8 bit scope, a 12 bit scope displays 16 dots. |
12 bits (4,096 dots) |
Enhanced Resolution
If a repetitive signal is displayed, the scope's resolution can be enhanced even further. An improvement of up to four bits can be achieved which can increase the resolution of a 12 bit scope to 16 bits. That means that up to 65,536 discrete levels can be displayed yielding an ultra smooth waveform. |
16 bits (65,536 dots) |
DC Accuracy
This is the absolute accuracy of a displayed DC level. If you read 10V then, if the accuracy is ±1% then the actual voltage could be any value from 9.9V to 10.1V. |
±1% of full scale |
±1% of full scale ±300 μV |
Input Sensitivity
Sensitivity shows what range of signals the scope can display (at full resolution). There are 10 vertical divisions thus the scope can display signals of 10 times these values (Note: the safe input voltage limit is ±200V). Where appropriate attenuators are used, this range can be increased. |
10mV / div to 40V / div |
2 mV/div to 10 V/div (10 vertical divisions) |
Input Ranges (full scale)
When you use the scope, you can set the vertical scaling in ranges. There is also an auto range that can set the vertical scale for you. The software will warn you if your signal is outside of the range you have selected. Again, appropriate attenuators can extend these ranges and you can define different probes which translate the ranges' scale or unit to suit the quantity being measured (e.g. amps instead of volts). |
±50 mV to ±200 V in 12 ranges |
±10 mV to ±50 V full scale, in 12 ranges |
Input Impedance
Input impedance means input resistance. It is important when you are measuring voltages where the source impedance is high. Some sensors have high resistance outputs and a low impedance input can produce an inaccurate measurement. Some scopes have 50Ω inputs and if a sensor with an output of 10V and an impedance of 1kΩ (1000Ω) was to be measured, the value read would be 0.476V, hopelessly inaccurate. The PicoScope with an impedance of 1MΩ (1 million ohms) would measure 9.98V, an error of only 2%. The input capacitance affects high frequency measurements because the impedance of a capacitor decreases as the frequency increases. It is therefore desirable to have a high input impedance and a low input capacitance. |
1 MΩ in parallel with 24 pF |
1 MΩ ∥ 19 pF |
Input Type
BNC means a special, bayonet connector used to handle high frequencies. Single ended means that only one input is provided per channel and voltages are with reference to its ground. Floating means that each input is separate from the other inputs and the rest of the scope. Each floating input needs its ground to be connected and you can use each channel independently without worrying that the grounds are connected to different places or voltages (up to 30V between channels). Floating inputs also increase reliability because the inputs are separated from the others and the PC. Floating inputs is a very valuable feature that sets the 4425A and 4225A PicoScopes apart from most other scopes. |
Floating, single ended, BNC Connectors |
Common ground, single ended, BNC Connectors |
Input Coupling
Input coupling (AC or DC) means that an input can accept DC values or can reject DC so that you can focus on the varying part of the signal. Sometimes a signal has a large DC offset with a small AC signal 'on top'. By selecting AC, the DC offset is removed and you can amplify the AC signal to see it much more clearly. |
Software selectable AC/DC |
Input Overvoltage Protection
The 4823 is only protected to ±100V. DC voltages in excess of ±100V or AC voltages in excess of 70V may damage the inputs. Always use attenuators when testing inductive devices such as ignition coil primaries, injectors and solenoids.
The absolute maximum voltage that can be applied to an input of the 4425 and 4225 is 250V! Although this is higher than most other automotive scopes can accept, please take note that if you try to measure an AC signal, like 240V mains, the peak value is far higher than 240V - actually 340V - which will damage the scope. The absolute maximum AC sine wave that the 4425 or 4225 scopes can withstand is only 175VAC (provided that there is no DC offset). For safety we recommend that you never apply more than 200V (140VAC) to any input. |
±250 V (DC + AC peak) |
±100 V (DC + AC peak) |
Input Common Mode
This specification is the absolute maximum voltage that can be applied between channel grounds. Channel grounds are not connected together on the 4425A and the 4225A, which means that they must always be connected when measuring. Unlike other scopes, they don't have to be connected to the vehicle ground which allows differential measurments. The voltage from ground to ground on any channel ralative to any other channel must not exceed 30V. The 4823 has common grounds which means that all grounds are electrically connected together. TIP you can use the maths channel feature (i.e. A-B) to do differential measurements, using two channels, to work around this problem. |
±30 V |
Common Grounds |