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GRT Sport 10.1 wiring question for analog inputs

DennisRhodes

Well Known Member
Looking at the Sport 10.1 Install manual for wiring up several analog inputs. Not much info on the how but a lot of info on the marketing!

For the older GRT EFIS interface they used 12vdc voltage source and a series 1K resister to one of the end terminals on a trim pot, the other end was ground and the third terminal or wiper was the input to the analog point on the EFIS.

On their EIS 4000 units they had a 4.3 regulated voltage that was applied thru a 10K resister much like the above and again the wiper was terminated to the EIS as an analog input.

The Hr and HXr GRTs series shows tieing the wiper and one end of the pot together and running that to the analog input, And ground the other end of the pot. Guessing the EFIS is suppling voltage to the external devise and that is done in the Menu set up along with what they are calling PULL UP RESiSTORS.

My question is :

Looking that this Sport 10.1 they really don't have a 4.5vdc regulated voltage to do it the old way nor do they show a typical method in the manual for how to do that analog input. Is it all done thru the Set UP? if so which connection is made to that analog input point ?

Without a 4.5 regulated voltage source on the pin out for that 10.1 Do I assume it is supplied from the EFIS and wire like the Hx or HXr series? Expecting the Menu and set up to fill in the blanks? A simple diagram in the install manual would make it really easy .
 
Looking at the Sport 10.1 Install manual for wiring up several analog inputs. Not much info on the how but a lot of info on the marketing!

For the older GRT EFIS interface they used 12vdc voltage source and a series 1K resister to one of the end terminals on a trim pot, the other end was ground and the third terminal or wiper was the input to the analog point on the EFIS.

On their EIS 4000 units they had a 4.3 regulated voltage that was applied thru a 10K resister much like the above and again the wiper was terminated to the EIS as an analog input.

The Hr and HXr GRTs series shows tieing the wiper and one end of the pot together and running that to the analog input, And ground the other end of the pot. Guessing the EFIS is suppling voltage to the external devise and that is done in the Menu set up along with what they are calling PULL UP RESiSTORS.

My question is :

Looking that this Sport 10.1 they really don't have a 4.5vdc regulated voltage to do it the old way nor do they show a typical method in the manual for how to do that analog input. Is it all done thru the Set UP? if so which connection is made to that analog input point ?

Without a 4.5 regulated voltage source on the pin out for that 10.1 Do I assume it is supplied from the EFIS and wire like the Hx or HXr series? Expecting the Menu and set up to fill in the blanks? A simple diagram in the install manual would make it really easy .
1. Only the EIS has a 4.8 (not 4.3) volt regulated source available. None of the EFIS units.
2. The analog inputs measure voltage. If you have a varying voltage to measure, just hook it up to an analog input, with PULL UP bias resistor off.
3. Many sensors are variable resistors, e.g., fuel sensors. To measure these you need to change the resistance to a voltage. At the same time, you need to keep the maximum voltage to less than the maximum the analog inputs can handle (I forget the number, is it 8 volts?). You can do this by:
A. Connect the 4.8 volts from the EIS to the ‘top end’ of the sensor, the ‘bottom end’ to ground, and the ‘wiper’ to an efis analog input, Pull Up off.
B. Connect the 14 volt buss voltage* to a resistor of value R, the other end of R to the top of the sensor, ground the other end, attach the wiper to an analog input, Pull Up off. You want the value of R to be large enough that you don’t exceed the max the inputs can handle, but not so large that the efis has to discriminate over a very small range of small voltages. Choosing R to be equal to the sensor resistance works well. *Also accuracy may be limited to how well the aircraft voltage regulator maintains an unvarying voltage, although you could install an independent regulator for this task.
C. The internal pull up resistors, when turned on, mimic (B). However, I think the internal resistors are large, like 10K, so method (B) may gain some more precision, although the analog inputs inherent accuracy seems to be very good.
Bottom line: it hardly matters. A, B, C all seem to give good results. Likewise, with B and C (but not A!) you can connect the pull up resistor to the top of the sensor, or to the wiper arm. You end up calibrating the result either way.
 
Pop them a quick email - you'll get a good written response to clarify.

The internal pull-up is essentially a software-controlled connection between the analog input connector pin to an internal voltage rail through a fixed resistor. This typically is used for sensing discrete inputs like switch closures. It was also used with the HX as you have pointed out - shorting the end of the potentiometer to the wiper and using that as the input, combined with the pull-up resistor resulted in the combination of an excitation voltage being applied to the potentiometer through a current-limiting internal resistor and the potentiometer acting like a variable resistance to ground, thus providing a software-readable varying voltage to the input of the EFIS.
 
Adding to the chorus...

Good contact at GRT: Jeff DeFouw, who knows this stuff well and is very responsive- [email protected]

I am very happy with GRT equipment and support, but their documentation is rather well known to be lacking. No documentation of analog inputs to speak of, anywhere. Since analog inputs can be configured identically to EIS auxiliary inputs you will eventually need to calculate an offset and scale factor, assuming a voltage input as previous posters described well. If there's any confusion about that Jeff is a big help.
 
Thanks for the replys and for the GRT contact. Bob, I like "A " above . I didn't want to wire to the EIS4000 but I do think I will locate the wire for the 4.8v regulated V on that EIS . Wire as you describe and ground the other end of the pot. Then run the wiper " green" to the Sport 10.1 analog point. that seems straight forward enough to me. Not sure what purpose the additional 1k resister serves shown ( on some dwgs) when using the 4.8v but easy enough to get to if it doesn't set up properly.

Thanks for the "input Knowledge"
 
A 1K resistor between the 4.8 volt power and the sensor protects the power supply, should there be a short in the sensor or associated wiring.
 
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To build on Bob's response, that 1K resistor does more than protect the power supply. It also increases the total resistance load on the power supply, thus acting as a current limiting device. That 4.8V output can't supply very much power so if one uses it to power several loads like 1K pots, one could easily overload the 4.8V supply. By installing a 1K series resistor between the 4.8V supply and each of those 1K pots the total current draw on the 4.8V line is drastically reduced.

Also, give serious consideration to using a separate ground return rather than airframe ground for sensors going into analog inputs. One wants to ensure the ground being provided to the sensor is exactly the same ground as either the EFIS or the EIS (whichever device you're using for its analog input). Using a 3-wire Mil-C-27500 twisted shielded three conductor cable will ensure a nice clean connection for excitation power, ground and signal being provided to the GRT gear.
 
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