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What does EXT/10 of this scope mean?

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student2005

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ext_trigger_div10.gif


There are two outputs at the front panel of an impulse voltage generator (IVG). One is trigger signal output (TSO, 0~12V), and the other one is the impulse voltage output (IVO, 0~12V). When the IVG releases an impulse voltage (width ~ 50us), the IVG will output a trigger signal at TSO.

The TSO and IVO are connected to the EXT TRIG input and Ch1 of Tektronix TDS3014B respectively. When EXT (see figure above) is selected and Single Sequence Button (single-shot acquisition) of the scope is activated, no signal is captured. When EXT/10 is selected and the level of trigger is set to 7V, the impulse voltage is captured.

Why EXT/10 is required in this measurement? Is the impulse voltage too high? Pls advise. Thanks.
 

Your TSO signal swings between 0V and +12V. You want to set the oscilloscope trigger level at approximately the halfway point, or +6V. This is not critical, anywhere within a few volts is probably fine.

Your Ext input lets you set the trigger level from -0.8V to +0.8V. That's not a good choice when you want a +6V trigger level.

Your Ext/10 input lets you set the trigger level between -8V and +8V. Now you can easily set the trigger level to +6V.
 

echo47 said:
Your TSO signal swings between 0V and +12V. You want to set the oscilloscope trigger level at approximately the halfway point, or +6V.

Your Ext input lets you set the trigger level from -0.8V to +0.8V. That's not a good choice when you want a +6V trigger level.

Your Ext/10 input lets you set the trigger level between -8V and +8V. Now you can easily set the trigger level to +6V.
Click to expand...
I thought Ext/10 attenuates the incoming signal by a factor of 10. So, the amplitude of the signal shown on scope is lower than the actual one, correct? A bit confusing here...
 

Yes, Ext/10 attenuates the "External Trigger Input" by 10, but that attenuator is independent from your scope's main input channels. Also, most scopes cannot display the External Trigger Input signal - that input is only used for trigger.

I haven't used a TDS3014B, but I've used a TDS3052 which is roughly similar.
 

student2005 said:
I thought Ext/10 attenuates the incoming signal by a factor of 10.
Click to expand...
It attenutates the signal connected to the EXTernal trigger input by a factor of ten but as its name suggests, that's the signal used to generate the trigger, and is generally NOT the signal you are trying to look at. The signal you want to view is likely on Channel A or B or 1 or 2, etc. Those are NOT attenutated by using the EXT/10, but instead by the setting of the appropriate Volts/Div knob.
 

Ooopss.... echo47 and mike65535, both of you were correct.

Actually my question is as follows. Say the amplitude of the signal connected to the EXT TRIG is 12V. After the internal attenuator of the scope(attenuated by a factor of 10), the amplitude of the attenuated signal should be 12/10=1.2V, right? But the trigger level is set to 7V (or half suggested by echo47). In this case, why the triggering is still working as the trigger level is ABOVE 1.2V?
 

The scope knows that you selected Ext/10 mode, so it does the math for you. It's wrong to mentally apply another factor of ten. When you set the scope's trigger level to 7V, then that's the actual trigger level at the input connector.
 

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