Fuel injectors

[Ryze]

When using the Modis to scope a fuel injector is a Attenuator??

[DougMontgomery]

Huh?......

[Ryze]

WoW!! I just re-read my own post. i guess I was in a hurry or something.

Anyways, when scoping a fuel injector, do I need to be using a attenuator of any kind (10:1, 20:1 etc)

[fueltrim01]

No, just follow component test meter of modis.

[Kris H]

Nope. The scopes votage scale range is suitable for all injectors that I'm aware of.

[twincity]

Ryze,
The last CTI class I went to, the instructor mentioned using an attenuator when you backprobed DIS coils. The attenuator is supposed to protect your scope in case the coil is shorted.

[Ryze]

They are mentioned in a few books that I have been reading, and when the Injector is shut off it does induce a high voltage, just wasn't sure if it would hurt the modis or not as I've never seen it mentioned on here or in the user manual at all
(its quite popular on the pico scopes)

Twincity. That is actually a good idea, and with the price of attenuators I suppose it wouldn't be a bad idea to get one. Sure beats having to pay the price to repair a Modis.
Also by your name, do you happen to live in the MN?

[DougMontgomery]

Ryze,
The last CTI class I went to, the instructor mentioned using an attenuator when you backprobed DIS coils. The attenuator is supposed to protect your scope in case the coil is shorted.

Twincity,

Not sure why he would say that? What a attenuator does for a scope is divide the incoming voltage by the attenuation factor (10:1 or 20:1 are the most common). So, if a signal under test was 500 VDC, then using a 10:1 attenuator would divide that by 10. This means the voltage at the input of your scope would be 50 VDC. So, if the signal your going to test exceeds your scope input max specified voltage, then you would want to use an attenuator.

Now, you stated if the coil was shorted, you wold need to use one. That should not be the case. The concern when testing inductive loads (coils - ignition, injectors) is the flyback (or inductive kick) voltage created when the primary circuit is interrupted (opened). A GM injector will typically create a 114-120 VDC flyback voltage and a typical igniton coil about 400 VDC or so (ignition coil voltages vary) . Now, the amount of inductance and dweel time determine the flyback voltage. If the coil is shorted, the flyback voltage will be greatly diminished, since the inductance will be low. Now the current will increase, but that does not flow through the scope, so your main concern is measured voltage for attenuator use.

Regards,

[Ryze]

Twincity,

Not sure why he would say that? What a attenuator does for a scope is divide the incoming voltage by the attenuation factor (10:1 or 20:1 are the most common). So, if a signal under test was 500 VDC, then using a 10:1 attenuator would divide that by 10. This means the voltage at the input of your scope would be 50 VDC. So, if the signal your going to test exceeds your scope input max specified voltage, then you would want to use an attenuator.

Now, you stated if the coil was shorted, you wold need to use one. That should not be the case. The concern when testing inductive loads (coils - ignition, injectors) is the flyback (or inductive kick) voltage created when the primary circuit is interrupted (opened). A GM injector will typically create a 114-120 VDC flyback voltage and a typical igniton coil about 400 VDC or so (ignition coil voltages vary) . Now, the amount of inductance and dweel time determine the flyback voltage. If the coil is shorted, the flyback voltage will be greatly diminished, since the inductance will be low. Now the current will increase, but that does not flow through the scope, so your main concern is measured voltage for attenuator use.

Regards,

Okay, if they the injectors are capable of 114-120v inductive kick, wouldn't this mean I need to use an attenuator for injectors on the modis?

[fueltrim01]

Modis lab scope goes up to 400 volts scale.

[jake63vw]

Yeah and even the Vantage Pro is a 200V Scale. I've scoped primary signal with peak detect and read above 200V, it won't fry the tool.

[Ryze]

Yeah and even the Vantage Pro is a 200V Scale. I've scoped primary signal with peak detect and read above 200V, it won't fry the tool.

My concern is on the top of the modis it specifically says 50/75v MAX.
The scale may be 400v, but does that mean it can actually take 400v?

[fueltrim01]

Read the user manual, page 11, Table 3-1 multimeter (75 VDC, 50 VAC). Scope page 12, Table 3-3, (400 VDC/AC). user manuals on line at SO.

[Ryze]

Read the user manual, page 11, Table 3-1 multimeter (75 VDC, 50 VAC). Scope page 12, Table 3-3, (400 VDC/AC). user manuals on line at SO.

Thank you.

I have the user manuals downloaded, and have scanned through the labscope manual, but must have missed that. I tend to skip over tables alot.