Practical Standalone Tuning: Arming Threshold
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Arming Threshold
02.30
| 00:00 | Arming a threshold is a setting in the ECU that is specific to reluctor sensors. |
| 00:05 | It's important to understand what it does and how it works as occasionally we may need to adjust this table. |
| 00:12 | A reluctor pickup inherently has quite a lot of background noise, but that doesn't present a big problem because the background noise is quite low relative to the size of the signal. |
| 00:22 | Both the signal amplitude and that of the noise will increase with engine RPM though so the ECU needs a way of ignoring the noise and only concentrating on the signal. |
| 00:31 | This is done with the arming threshold table which is a 2D table of arming voltage versus RPM. |
| 00:38 | Basically, the ECU waits until it sees the voltage on the trigger input rise above the arming threshold. |
| 00:44 | At this point the trigger input is armed and ready. |
| 00:47 | When the voltage drops back through zero volts this is the point where the ECU triggers. |
| 00:53 | Now if the arming threshold is set too high, the trigger input may never reach it hence the ECU will ignore all trigger inputs. |
| 01:01 | This is especially an issue at low RPM when the trigger amplitude might be quite low. |
| 01:06 | On the other hand, if the arming threshold is set too low, background noise may be enough to make the ECU arm resulting in an erratic RPM signal. |
| 01:15 | The rule is to set the arming threshold at 1/3 of the peak signal voltage at each RPM point in the arming table. |
| 01:23 | This is pretty difficult without the aid of an oscilloscope so you can actually measure the signal though. |
| 01:28 | Generally, the default arming threshold will be fine for most stock engines, but occasionally you may need to adjust the table. |
| 01:35 | Without a scope you're not going to know if the table needs to be increased or decreased. |
| 01:39 | So you're going to need to try both options, and see which works to remove your triggering issue. |
| 01:45 | Generally, if the arming threshold is too low, the ECU will receive too many trigger events, and this produces an erratic RPM trace. |
| 01:54 | You can often see this in datalogs where the RPM is reaching unrealistic peaks of say 20,000 RPM in an instant. |
| 02:01 | If the arming threshold is too high, the ECU won't see any RPM at all. |
| 02:06 | The tip here is to start with an arming threshold of around 0.3 to 0.5 volts at 0 RPM, and increase this smoothly to around 4 volts at 7,000 RPM. |
| 02:17 | If you make any adjustments, I suggest making them at 0.5 volt increments, and generally you won't need to increase your maximum above 5 volts. |
