OXS voltage too high, frequency is to high as well

[Ameer Antar]

How are you measuring o2 signal? Where are you monitoring the voltage from? 
AC or DC setting? Is the meter calibrated. Usually the o2 signal is jumping 
around so it's nearly impossible to monitor on a digital meter and even 
analog ones b/c sometimes the needle can't move that fast. The o2 signal is 
best viewed using a gauge or what I've recently done is just make one up 
from a 2-3 chips. There is a special bar-graph chip that will display 
voltage level through a set of LED's set up as a bar graph. The chips have 
decent refresh, so you can actually see detailed movement. Each chip drives 
10 led's, but you can hook them up together to use 20, 30 or whatever # of 
LED's. The more LED's the more resolution, b/c then each LED represents a 
smaller range of voltages. The chip is the LM3914. The datasheet is here: 
http://www.national.com/ds/LM/LM3914.pdf

I'm not sure what you mean about the duty cycle. DC is measured in %, not 
Hz. The Hz [frequency] is not what you want to know. You need to monitor 
D.C. %, which is just the ratio of time on to time off. Basically if you 
put the FV signal on a scope, it would look like a square wave. For a 
certain time the signal is low [valve is off] and the next portion is high 
[valve is on]. At 0%, the signal is completely off all the time. At 50%, 
the time off = time on. At 100% the signal is always on. The freq. valve 
line is quite noisy. I've seen it on a scope and you have to adjust your 
meter to set the proper threshold. This threshold sets all the signal below 
that point as low and above that point to high. Adjusting this may give you 
the real DC reading, b/c there's a bit of noise. Another possibility is to 
connect the neg. side of the meter to ground, and on the pos. side, instead 
of connecting it directly to the test plug on the car, connect a capacitor 
in-between the pos. side on the meter and pos. side of test plug. The cap. 
can be found at Radio Shack and should be at least 100uF [micro-farad]. The 
cap will filter out some of the noise and any DC current in the line, which 
you don't want. But the cap. can also filter out the signal depending on 
the frequency and the load of the meter. If you use a small cap, it will 
begin filtering out any low frequency signals. Using a large cap like 
100-470uF will only filter very low unimportant frequencies like .01-.2 Hz. 
I'm just curious where do you get a value of 2Hz, in the Bentley? What is 
the freq. your getting? Do you mean D.C.?

-ameer


At 08:34 PM 12/12/2000 , you wrote:
>Can someone come up with any idea why my OXS sweeps between ~15mV and
>2.2V,  not between  0.1 and 1 V as it should do?  The frequency ECU
>changes FV duty cycle is much high then 2 Hz as it should be.  At least
>I can not see duty cycle on DMM without pressing hold button. Same
>question: why could it do that?
>
>Thanks.
>Konstantin Bogach.
>200tq 89