MAF voltages
05-05-2005, 07:18 PM
#1
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MAF voltages
For those interested.
I just got my logworks rigged up for Mass Airflow voltage. Just tapped 2 wires off the MAF sensor and plug it in. Pretty easy.
This was a 20mph ish roll on to 100.
Log works wont register anything over 5 volts (but my video camera does)
I need to figure out how to make a voltage divider now...DR Bob?
I just got my logworks rigged up for Mass Airflow voltage. Just tapped 2 wires off the MAF sensor and plug it in. Pretty easy.
This was a 20mph ish roll on to 100.
Log works wont register anything over 5 volts (but my video camera does)
I need to figure out how to make a voltage divider now...DR Bob?
05-05-2005, 07:33 PM
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Hmmm, I would have expected your MAF voltage to go higher.
What did you want the Voltage divider for ?
Bit too late for J Speake to be up and about I guess !
Chris
What did you want the Voltage divider for ?
Bit too late for J Speake to be up and about I guess !
Chris
05-05-2005, 08:09 PM
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Aggghhh well that helps. Got to be careful you don't upset the voltage divider inside the LH, the following diagram should work and not upset the LH too much.
You can always design a small circuit with a high impedance op-amp but for a quick and dirty .....
Chris
You can always design a small circuit with a high impedance op-amp but for a quick and dirty .....
Chris
05-05-2005, 09:05 PM
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Thanks Chris
lots of Google stuff
http://www.sengpielaudio.com/calcula...agedivider.htm is one.
On the diagram above...the items inside the dotted line represent items internal to the LH?
lots of Google stuff
http://www.sengpielaudio.com/calcula...agedivider.htm is one.
On the diagram above...the items inside the dotted line represent items internal to the LH?
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05-06-2005, 05:56 AM
#8
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The MAF output impedance is less than 10 ohms, so the only problem is not having too high an impedance to feed the data logger, compared to its input impedance.
Also with 2 x 1Meg resistors, there is a chance of noise pickup. The data logger may also have an input impedance that is similar to 1Meg.
I would suggest making those two 1Meg resistors 10k each. This won't upset the LH.
Tony PM'd me to say he measures 5.7v max - on reflection this sounds a bit on the low side, so I suspect the data logger is loading the divider.
Also with 2 x 1Meg resistors, there is a chance of noise pickup. The data logger may also have an input impedance that is similar to 1Meg.
I would suggest making those two 1Meg resistors 10k each. This won't upset the LH.
Tony PM'd me to say he measures 5.7v max - on reflection this sounds a bit on the low side, so I suspect the data logger is loading the divider.
05-06-2005, 12:22 PM
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I wish i was this smart and could take credit for this you EE guys are scary! 
.......
Its from Klaus at Innovate Motorsports, they make the LM1 and the data logger.
(he Chimes in here now and then)
I just built a small circuit as described in the last paragraph then used this website to plug in kown voltages ....plotted the stuff and tossed it into the Logworks config table.
http://hyperphysics.phy-astr.gsu.edu...ic/voldiv.html
input......... Volt
0......... 0
0.1......... 0.064
0.5......... 0.319
1......... 0.639
2......... 1.279
3......... 1.919
4......... 2.559
5........ 3.199
6......... 3.839
7......... 4.479
8......... 5.119
With my mulitmeter on the wires it indicated 1.58 when i turned the key...so did log works. Its close enough for what i need anyway.
Proof certain that the mass airflow sensor WILL read over 5V! I think its just that the LH doesnt know what to do with anything over 5?
HTH for any one else. I have the info i need now
.......Its from Klaus at Innovate Motorsports, they make the LM1 and the data logger.
(he Chimes in here now and then)
I just built a small circuit as described in the last paragraph then used this website to plug in kown voltages ....plotted the stuff and tossed it into the Logworks config table.
http://hyperphysics.phy-astr.gsu.edu...ic/voldiv.html
input......... Volt
0......... 0
0.1......... 0.064
0.5......... 0.319
1......... 0.639
2......... 1.279
3......... 1.919
4......... 2.559
5........ 3.199
6......... 3.839
7......... 4.479
8......... 5.119
With my mulitmeter on the wires it indicated 1.58 when i turned the key...so did log works. Its close enough for what i need anyway.
Proof certain that the mass airflow sensor WILL read over 5V! I think its just that the LH doesnt know what to do with anything over 5?
The actual values are determined by the output inpedance of the source and the input impedance of the destination. The voltage divider puts a load on the source. This could change the voltages. The input impedance of whatever receives the divided signal puts a load on the divider circuit and could also change the voltages. A good rule of thumb is to make the sum of the divider resistors bigger than 10x the source impedance of the originating device. Also make the resistance formed by putting the divider resistors in parallel (output impedance of divider) smaller than 1/10th the input impedance of the receiving device, which in the case of the LMA-3 is about 1 MOhm.
Here are the formulas used, where Vin is the input voltage to the divider, Vout is the output voltage, R1 is the resistor connected between output of the source and input of the receiving device, R2 is connected between input of the receiving device and ground.
Vout = Vin * R2 / (R1 + R2)
Input impedance of divider (should be at least 10x the source impedance of the originating device):
Rin = R1 + R2
Output impedance of divider (should be smaller than 100kOhm, which is 1/10th of the input impedance of the LMA-3)
Rout = R1 * R2 / (R1 + R2)
Standard resistors come in certain fixed values in a series. The standard E24 series, which is what you can get just about anywhere, consists of:
1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2 and 9.1 and powers of 10 thereof.
Assuming an output impedance of 10 kOhm for a MAF sensor with 7V output, you would use R2 = 100k, R1 = 56k. This divides the 7V by a factor of 1.56 resulting in a 4.48V output for a 7V input, leaving some headroom for tolerances. It puts a load of 156k on the MAF sensor (15.6 times assumed source impedance) and provides a source impendance of 35.9k Ohm for the LMA-3, which is 0.0359 the input impedance of the LMA-3, which is smaller than the 1/10th of the rule of thumb as required.
Here are the formulas used, where Vin is the input voltage to the divider, Vout is the output voltage, R1 is the resistor connected between output of the source and input of the receiving device, R2 is connected between input of the receiving device and ground.
Vout = Vin * R2 / (R1 + R2)
Input impedance of divider (should be at least 10x the source impedance of the originating device):
Rin = R1 + R2
Output impedance of divider (should be smaller than 100kOhm, which is 1/10th of the input impedance of the LMA-3)
Rout = R1 * R2 / (R1 + R2)
Standard resistors come in certain fixed values in a series. The standard E24 series, which is what you can get just about anywhere, consists of:
1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2 and 9.1 and powers of 10 thereof.
Assuming an output impedance of 10 kOhm for a MAF sensor with 7V output, you would use R2 = 100k, R1 = 56k. This divides the 7V by a factor of 1.56 resulting in a 4.48V output for a 7V input, leaving some headroom for tolerances. It puts a load of 156k on the MAF sensor (15.6 times assumed source impedance) and provides a source impendance of 35.9k Ohm for the LMA-3, which is 0.0359 the input impedance of the LMA-3, which is smaller than the 1/10th of the rule of thumb as required.
HTH for any one else. I have the info i need now
05-06-2005, 12:23 PM
#10
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Tony,
Your AFR curve is nice and flat now, did you go back to the bigger injectors? (ref an earlier thread where we got into a discussion on maxing out injector duty cycle and linearly rising AFR curve)
Jason
Your AFR curve is nice and flat now, did you go back to the bigger injectors? (ref an earlier thread where we got into a discussion on maxing out injector duty cycle and linearly rising AFR curve)
Jason
05-06-2005, 12:39 PM
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Originally Posted by Mongoose
Tony,
Your AFR curve is nice and flat now, did you go back to the bigger injectors? (ref an earlier thread where we got into a discussion on maxing out injector duty cycle and linearly rising AFR curve)
Jason
Your AFR curve is nice and flat now, did you go back to the bigger injectors? (ref an earlier thread where we got into a discussion on maxing out injector duty cycle and linearly rising AFR curve)
Jason
I could put in 60...100lb injectors and they would still max out at 100 duty cycle...i would then have to adjust the fuel pressure to get the mixture correct.
I wish i would have had this device earlier. I would have enjoyed logging a NA car. I believe the stock set up would eventualy max out as well, but since you are NA the increase in airflow isnt there to send the MAF votlages up to the level we see in boosted cars. Hence you wont see 100% duty.
I believe that is the logic. Im sure Marc T would have a good idea for the NA cars with power level and CFM they are at.
Pretty interestig $hit though how it all works!
Tony PM'd me to say he measures 5.7v max - on reflection this sounds a bit on the low side, so I suspect the data logger is loading the divider
Would there be any difference in the fact that on a VORTECH it "blows through" the MAF where as on a "TwinScrew" the air is "sucked through"
Im imagine my charge temp is a bit lower when measured at the MAF?
Glad you got something that worked, now go get some new graphs !
05-06-2005, 02:19 PM
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Hi Tony,
The standard LH ECU max's out at about 5.6v. With my EPROM emulator we have found a way to map up to MAF = 6.1v without any change to the hardware.
What resistor values did you use in the end ?
It doesn't make any difference to the MAF if you suck it or blow it ! Charge temp doesn't make any difference to the MAF figures. The MAF measures MASS airflow so automatically compensates for charge temperature etc.
5.7v is probably right for your boost level, I think I was confusing it with Lag's 11psi car.
The standard LH ECU max's out at about 5.6v. With my EPROM emulator we have found a way to map up to MAF = 6.1v without any change to the hardware.
What resistor values did you use in the end ?
It doesn't make any difference to the MAF if you suck it or blow it ! Charge temp doesn't make any difference to the MAF figures. The MAF measures MASS airflow so automatically compensates for charge temperature etc.
5.7v is probably right for your boost level, I think I was confusing it with Lag's 11psi car.
05-06-2005, 06:13 PM
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The standard LH ECU max's out at about 5.6v. With my EPROM emulator we have found a way to map up to MAF = 6.1v without any change to the hardware.
but way over my head though on how you do this stuff.
What resistor values did you use in the end ?
5.7v is probably right for your boost level, I think I was confusing it with Lag's 11psi car
, i will know what to look for 
this is a quick and dirty of the set up