Help with a real EGT indicator

[frazer]

Hi!

I need help with a EGT indicator that I've bought of eBay.

I've opened it to find out that the pins F and J are backlight, but I have no idea what the rest of the pins does and what "data" is needed to get the needle to move.

Any ideas?

5953
5954
5955

[jonesthesoftware]

You could try contacting the manufacturer ....website below Explain that it is for home use only though! Try different departments as some people are more helpful than others, but that's human nature.

http://www.rogersonkratos.com/support.html

regards
geoff

[frazer]

You could try contacting the manufacturer ....website below Explain that it is for home use only though! Try different departments as some people are more helpful than others, but that's human nature.

That's a good idea, definetly worth a try!

Thanks!

[frazer]

You could try contacting the manufacturer ....website below Explain that it is for home use only though! Try different departments as some people are more helpful than others, but that's human nature.

I've got an answer quite quickly:

The cost for an issue of a CMM for this part is $500.00.

I don't even know whan a CMM is, but I don't think I want to pay 500$ to find out :roll:

[mach7]

For what application are you using the gauge for? You might want to consider driving the needle with an RC servo and gutting out the rest of the electronics...

[frazer]

For what application are you using the gauge for? You might want to consider driving the needle with an RC servo and gutting out the rest of the electronics...

It's to be used as an EGT indicator for the APU in the overhead of a 737 simulator. I would really like to drive it using the original motor, beats RC-servo movement by miles.

[737NUT]

That gauge requires Mv dc to function as it hooks directly to the EGT thermocouple. You could drive it using a servo to turn a potentiometer and a voltage divider with a few cap's to smooth out the output.

Rob

[frazer]

That gauge requires Mv dc to function as it hooks directly to the EGT thermocouple. You could drive it using a servo to turn a potentiometer and a voltage divider with a few cap's to smooth out the output.

Thanks for the input, that was what I suspected. Now the problem is to know what pins to use in the cannon connector at the back.

[jonesthesoftware]

to protect your instrument buy a cheap K type thermocouple ( lots of suppliers sell 1 metre ready made wire type versions very cheaply). Put the end which has the wires soldered together into a flame from a cigarette lighter or gas flame of the cooker(stove) This will generate the correct amount of millivolts but at such a low current it will not destroy any circuits if it is connected to the wrong pins. Use this thermocouple to test each pair of pins in the connector until the EGT reads 400-500 degrees. Voila you've found your pins. You may need to do the exercise twice with the connections reversed to get the right polarity. I'm assuming the EGT instrument does not require an external power supply for internal amplifiers! Hopefully the instrument indicates directly from the millivolts of the T/C
kind regards
geoff

[737NUT]

If you take it apart it is is to tell which ones are the correct ones. Most of the pins are not even used. In the EGT's I have had just 4-6 pins were used. Remember the polarity must be correct as stated.

[frazer]

If you take it apart it is is to tell which ones are the correct ones. Most of the pins are not even used. In the EGT's I have had just 4-6 pins were used. Remember the polarity must be correct as stated.

This one is really full of components and at least 8 pins are in use (2 for backlighting though), very compact and hard to tell which one does what. According to the website, it contains a lot of filters etc, which may explain the amount of components.

A wild idea of mine was to use a servo-card (opencockpits or phidghets) to get the voltage needed. If I connect the negative pin and the data-pin, i should get voltages near these. Anyone know exactly what voltages I would end up with? I think it's working with PWM from 0,4 to 25ms.

[jonesthesoftware]

Hi
You'll get 5 volts because PWM means PULSE WIDTH MODULATION which means the output switches between almost 0 and almost 5 volts with controlled width pulses. This series of pulses controls the servo motor by the duration and spacing of the pulses NOT the voltage. Make a voltage divider using a potentiometer and 1 series resistor (connected on the positive side of the pot) this is to ensure your voltage never gets too high when the pot is at the max of the stroke. Calculate this series resistor to give a maximum of say 200mVolts when the pot is at max, then you can control between 0 and 200 mVolts if you are testing for the thermocouple
regards
geoff