:::RHMT::: Real Home Made Turbo
General Category => Engine Management => Topic started by: lilpooh21186 on March 28, 2009, 10:11:35 PM
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This Was Taken From the Logworks Datalogging Manual.
Most sensors requires a ground connection. The voltage output of the sensor is referenced to that
ground. If the device measuring the sensor is connected to a different ground, the voltage
difference between the grounds can shift the sensor output voltage relative to the measuring
device. Some measuring devices, like the LMA-3, have differential inputs to compensate for that
offset. The negative side of a differential input is NOT a ground. It is intended to be connected to
the same ground as the sensor. A measuring device with a differential input measures the
difference between its own ground and the sensor’s ground on the negative input and subtracts
the difference from the measured voltage on the positive input to compensate for the ground
offsets. The hookup from a differential input requires two wires. One for the signal itself and one
for the ground reference. The ground reference input (typically named CHx-) goes to the
grounding point of the sensor.
Ground offsets are especially problematic for resistive and voltage output sensors. They are not
so important for frequency or duty cycle based sensors. For a measuring device with common
ground, like the LMA-2, it is best to ground all sensors at the same point where the measuring
device itself is grounded.
Ground offsets can also affect frequency or duty cycle based sensors. Typically when measuring
a frequency, the signal is measured as ‘high’ or ‘low’ depending on the measurement device’s
high-low threshold. In the LMA-2 or LMA-3 the threshold is 1V for the LMA-2 or 2.5V for the LMA-
3. Ground offsets of 1V or 2.5V will not allow the device to measure correctly.
Another problem can be ‘ground bounce’. If the signal generating device (for example an ignition
system) creates very high current pulses, it’s ground can momentarily ‘jump’ over the threshold of
the measuring device because of the high current. These ‘ground-bounce’ pulses are measured
as false frequencies and can interfere with the measurement.
Another problem in sensor hookup is called ‘induced noise’. In an engine compartment very high
current pulses are routed many different places. These current pulses can come from the
LogWorks3_Manual_1.01.doc
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injectors, ignition system or alternator. Any (changing) current flowing through a conductor
creates a changing magnetic field. A changing magnetic field intersecting another conductor (for
example the sensor wires) will create a voltage along that conductor. This voltage is added as
noise to the sensor signal. This is how an antenna for radio signals works as well.
By twisting the sensor output and sensor ground wire together, that induced noise can be
minimized. Each twist creates a wire loop acting as small antenna to pick up the induced noise.
BUT, the noise induced in each loop changes polarity from loop to loop. This way each twist-loop
cancels out the noise from the previous loop. The tighter the twist, the more cancellation can be
achieved.
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Good post. :)
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yea i was reading on it i never relized that the info i was getting from sensors was a calculation between the difference of a power and ground
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Ding ding ding.
You Honduh guys need to make sure you ground your widebands to the thermostat housing if you are logging wideband via the ECU.
Grounding to the block, trans, chassis, etc introduces a resistance in the ground path, which lowers the voltage read at the ECU. For the popular wideband voltage outputs this skews the logged wideband reading to the rich side of things.
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JD could i just tap into the wire that goes to the therm housing from the ecu? i just bought the lm-2 its gunna be a bitch running wires all the way to the engine bay.
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Make some jumper wires with aligator clips. Make it easy to get on/off. It's not a big deal.
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When I first did mine I bought a pc power supply extension cord from radio shack. It's like 4 wires male to female plug, I cut it in half and soldered one side to my lc-1 and the other into my car. My friends got the same plug so when they wanted me to fuck with their car I could plug right in.
I'll do aligator clips next time. Too much of a hassle splicing into harnesses, though now when I don't want to fuck with someone's car I use it as an excuse that my wideband won't plug in and it would be too much hassle to change it.
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ok i never thought about using aligator clips.
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Ding ding ding.
You Honduh guys need to make sure you ground your widebands to the thermostat housing if you are logging wideband via the ECU.
Grounding to the block, trans, chassis, etc introduces a resistance in the ground path, which lowers the voltage read at the ECU. For the popular wideband voltage outputs this skews the logged wideband reading to the rich side of things.
And can also cause current from high power devices to flow through low current devices. Which is what causes sensor noise.
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JD, what about using a relay for a permanet install? I have a relay wired directly to the battery for power and grounded to the thermosat housing, but couldn't you just do it from either there or from ground on the battery on a setup like that?
I always leave the wideband in the car and didn't like the idea of having to clip on alligator clips or hit an extra switch everytime i start the car.With the relay it starts and shutsdown like normal
For a tuning rig that's going to move around alot clips are the way to go.I bought an extra power wire for my lm-1 so i can just leave the relay setup in my car and then still have the clip setup for other cars.
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JD, what about using a relay for a permanet install? I have a relay wired directly to the battery for power and grounded to the thermosat housing, but couldn't you just do it from either there or from ground on the battery on a setup like that?
I always leave the wideband in the car and didn't like the idea of having to clip on alligator clips or hit an extra switch everytime i start the car.With the relay it starts and shutsdown like normal
For a tuning rig that's going to move around alot clips are the way to go.I bought an extra power wire for my lm-1 so i can just leave the relay setup in my car and then still have the clip setup for other cars.
Dunno about LM-1's, but LC-1's you have to follow the directions 100.000000000000000000000000% or it won't work correctly. Mine's hooked up EXACTLY as outlined in the instructions included with the wideband and has operated trouble free for over a year now.
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That's what i liked about the lm-1 vs the lc-1. The lm-1 is simple. 1 Power 1 ground 1 analog output/ done.
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JD, what about using a relay for a permanet install? I have a relay wired directly to the battery for power and grounded to the thermosat housing, but couldn't you just do it from either there or from ground on the battery on a setup like that?
I always leave the wideband in the car and didn't like the idea of having to clip on alligator clips or hit an extra switch everytime i start the car.With the relay it starts and shutsdown like normal
For a tuning rig that's going to move around alot clips are the way to go.I bought an extra power wire for my lm-1 so i can just leave the relay setup in my car and then still have the clip setup for other cars.
i personaly use the aem uego and it sucked but its simple. I bought the lm-2 For logworks and the ease of the interchangeablity between cars, because im tuning others now. Im to kind of scetchy about the aligator clips but its easier than hacking up the owners harness ill just run the clip to the therm housing and back in the car tie all grounds to that. quick and easy hopfully it will only take me 15min to setup for a tune.
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Ding ding ding.
You Honduh guys need to make sure you ground your widebands to the thermostat housing if you are logging wideband via the ECU.
Grounding to the block, trans, chassis, etc introduces a resistance in the ground path, which lowers the voltage read at the ECU. For the popular wideband voltage outputs this skews the logged wideband reading to the rich side of things.
Thanks for the info I have been running the ground to my WB to the chassis at same place as my MSD box ground. :?:
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JD, what about using a relay for a permanet install?
Relays are used to switch things that suck some current, so that the source of the "on signal is protected from large current (dash switches, ECUs, etc). A wideband uses less power than a factory CD player, makes no sense to use a relay when switched power works fine.
That being said you won't hurt anything, just make sure the relay is on the power side. Relay contacts end up like points in pre-electronic ignition systems, they get scorched and have a little resistance across them.
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I more so just used the relay to switch on and off the wideband with the car since at first it was hardwired positive and negative to the battery.
I did have a switched 12+ from the cigg lighter as power before I did the relay/hardwire but that didn't seem like the best place to me and I keep hearing positive and negative things about using the ecu 12 volt power.
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I more so just used the relay to switch on and off the wideband with the car since at first it was hardwired positive and negative to the battery.
I did have a switched 12+ from the cigg lighter as power before I did the relay/hardwire but that didn't seem like the best place to me and I keep hearing positive and negative things about using the ecu 12 volt power.
you could always wire up to the ignition power thick black/yellow wire usually top of the fuse box works great