Wideband 02 install questions

[Marv [uk]]

any spec on the zener diode yet?

[Marv [uk]]

Just one more piece of information required to get it straight in my head...

The gauge is compensated for EGT as in if it's 30 degrees outsides but the EGT is 650 degrees, the gauge automatically compensates for ambient temperature showing the EGT as an absolute temperature.

Question - Is this compensated to the temperature at the gauge (inside the gauge) or does it require a temperature compensated K thermocouple cable?

[rob@vems.co.uk]

The thermocouple has to use k-type cable all the way through or it forms a cold junction at the dissimilar metal joint and starts messing with the temperature reading.  The temperature reading is the temperature at the tip of the sensor.

[Marv [uk]]

The thermocouple has to use k-type cable all the way through or it forms a cold junction at the dissimilar metal joint and starts messing with the temperature reading.  The temperature reading is the temperature at the tip of the sensor.

I sort of understand all this

the K thermocouple measures the temperature difference between the two ends of the twin cable by producing a millivoltage current depending on the temperature gradient. This is casued by the dissimilar metals. Know the voltage, know the temperature difference. Cold junction compensation references the ambient temperature at the cold junction which in turn references the cold junction temperature to "a bucket of ice" or 0 degrees C. Because K thermocouple properties are well known, electronics can be set up to measure a reference voltage of the cold junction against the known voltage of a k type at 0 degrees so the electronics can then work out exactly what the real temperature in degrees celcius is being measured at the hot end

The display on the gauge then is electronically wombled with and shows the actual temperature in degrees celcius. I.e. you can get a thermometer and read the same temperature (if it doesn't melt) at the hot end if you so fancied making the effort

Thermocouple cables can be extended provided that the extension cable is of the same stuff and polarity and that the junctions are made on a "similar material" so there is no temperature difference between the + ve and - ve wires to monkey about with the data

The question really is do I go out and buy a standard K thermocouple with 2 wires, or do I have to get a temperature compensated cable? Does the gauge itself carry out the compensation or does it have to be supplied with the induced voltage already compensated to freezing point? I'm currently assuming the that the gauge does, but i've read 2 different explanations on the Wiki and it's confused me

I've got a supplier of K thermocouple cable (with american insulation) complete with a 14mm spark plug end and an extension cable (again american spec insulation) and a couple of proper connectors lined up, but it's all non compensated cable. Is it the right stuff? 

Sorry for being a PITA and thanks for humouring my stupid questions

[rob@vems.co.uk]

Use standard normal k-type wire, the gauge has an internal temperature measurement which I understand the AD597AR chip uses to compensate.

[Marv [uk]]

Corking!

Got my WBo2 gauge and it looks great and everything is there. Chuffed to bits

But the instruction SUCK

Still, i'll get there really looking forward to having it all plugged in. Going off to get a couple of grommets now :D

[rob@vems.co.uk]

Even these instructions suck:
http://www.vems.co.uk/VEMSWB/UserGuide/README.html

If you have any questions on information that is missing please ask and I can make the documentation better.

[Marv [uk]]

Not exactly sucky Rob , much better than the ones that don't even come in the box for crying out loud!

The wiki is pants, there is no two ways about it. What this product needs is a decent wiring diagram that does not continually go on about R232 this and that when it doesn't even show what they all are

Simple would be good

on the separate wiring harness, connect the red to the switched live ignition at the fuse box. connect the blue to a suitable earth

connect the o2 sensor connection as the diagram shows on your instructions cos thats a good one. the ones in the box were crap and obviously babelfished

what is the other cable for? I know it's for connecting to an engine management box but it never actually says what it for

Someone REALLY needs to write proper instructions for this as the wiki is crap and speaks in technobabble that even a geek friend of mine has difficulty with.

I really really REALLY hope the gauge is better than the instructions else i'll be fuming!

[Bat]

Hi,
The Gauges are good, I've sold a couple to some very impressed customers
Cheers,
Gavin

[rob@vems.co.uk]

One cable is for power and external connections.
One with a 9pin plug is to connect to a serial port on a PC/Laptop.
Then theres the wideband connector, and finally the green and white thermocouple wire.

[Marv [uk]]

Well I finally got it all installed and connected up and I is a very happy bunny

Feedback!

For future reference a 5m cable is perhaps half a meter too short for a VW camper given the length of the wideband sensor cable but I got mine to work with no splices The rubber boot is most definitely impossible to thread through the wireways on a bus so has to come off, might as well not put it on. Had a bit of difficulty threading the 6 crimps through at times and they could do with a bit of staggering but no big deal.

All in all, a very simple install complicated by the type of vehicle

One problem though...... the EGT just will not hold still on a number and fluctuates wildly. On start up while the o2 sensor is heating the EGT fluctuates between say about 200 and 400 *C then as the sensor heats, the value drops down to 0 and fluctuates up to about 100. The fluctuations are rapid, say 5 or 6 a second and are seemingly random. I've been through the system from end to end and, Although I have 2 thermocouple connectors in there, all polarities are correct. When the thermocouple is diconnected, the gauge reads a steady 1174*C. I have a copper ring K thermocouple from the states clamped beneath #3 spark plug which is connected to a 15 foot extension which is then connected to the cable in the back of the gauge.

Any ideas what the problem is?

Cheers

[rob@vems.co.uk]

Good news on the install.
As for the thermocouple reading, I've not seen anything like that before, do you think you could test the thing by connecting a thermocouple directly to the gauge?  It uses such small voltage differences, and the cable is so long that it could potentially be acting as an antenna for noise.

[Marv [uk]]

Good news on the install.
As for the thermocouple reading, I've not seen anything like that before, do you think you could test the thing by connecting a thermocouple directly to the gauge?  It uses such small voltage differences, and the cable is so long that it could potentially be acting as an antenna for noise.

Funny you should say that but that is what I was originally thinking as it is so close to a spark plug.

Plugging the thing directly into the gauge is a bit of a no no. It took me for f'n-ever to get it in there as #3 is a pig to reach, especially with twin carbs so i'll not be taking it out in a hurry!! Any ideas for some electronic shielding? bit of stainless braiding perhaps?

[rob@vems.co.uk]

If you connect the two wires on a k-type together they create a thermocouple, how is the extension connected to the thermocouple wires that come out of the gauge?

[Marv [uk]]

If you connect the two wires on a k-type together they create a thermocouple, how is the extension connected to the thermocouple wires that come out of the gauge?

It's got a proper K type thermocouple connector on it as per the destructions

I checked the end of the extension after i connected it but before i threaded it through all the really hard to get places beneath the floorpan and when touched together, the two wires registered a steady 23 degrees which was a few degrees higher than ambient but probably the same as my finger temperature so I was happy that it all worked and was connected properly.

The other thing I was thinking was that, as the thermocouple cable is laid alongside the power cable for the wideband, interference from the wideband heater cable would explain the weird behaviour of the thermocouple as it's high during heating, then falls off to zero ish after the heat cycle has finished. They really are side by side for nearly 5 meters. They are also very close to the main power cable.

Hmmmm, I think, first, I'm going to have to separate the thermocouple cable from the wideband cable for as much distance as I can and see if that has any effect. If it doesn't then I'm going to have to think of something else.

As a minimum, i think the 1m thermocouple itself, from the end of the extension to the spark plug, needs a steel overbraid to shield it from the ignition leads though.

Perhaps Mr Hungarian needs to do a bit of research to see just how the o2 cable interferes with the thermocouple cable just so it can be added to the instructions or perhaps shielded at source.