New sensor with xDrip+ is off with its readings

Hi all, I had my first sensor last 18 days on xDrip+ after switching it from the Dexcom app (was on that for 6 days before I switched), and it needed calibrations now and then. With the Dexcom app and the exact same sensor the readings where spot on when I tested it just to see (since it was my first time), but not when I switched to xDrip+.

I just put in a brand new sensor last night, and from the beginning my BGs (tested with Freestyle Lite) have been notably off from xDrip+ readings again, by an amount that makes a difference. And after I did the initial calibration last night because it was wrong, it was wrong again this morning when I woke up and tested it, so I did the override calibration thing…which will probably be inaccurate again if my experience with the last sensor with xDrip+ is any indication. Again: My first sensor was spot on with the Dexcom app but was off with xDrip+ after switching to it, so I don’t think it’s the sensors.

Is there a reason why I need to even calibrate with xDrip+ and G6 sensors after I put the new sensor in? What could I be doing wrong with the initial source bonding to the sensor? I followed the instructions that I’ve seen here exactly by using the source wizard. Is there a way to re-do it so that it reads as consistently accurately as the Dexcom app did (which didn’t need calibration)?

If I need to calibrate frequently then that would negate one of the biggest benefits of the G6 and I won’t be able to use xDrip+, so I dearly hope I’m just doing something wrong because otherwise it’s far superior…but this is a major thing to need to worry about.

EDIT: I just sent the error report through xDrip+ so hopefully someone can take a look at it and I can get this fixed – there are a huge amount of errors since I started using it almost two weeks ago, but I don’t know what they mean or how significant they are. But if there are suggestions here on why this problem is happening, I’m all all ears. :slight_smile:

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I will say that we are G6 users, but not XDrip+ users. We have never calibrated a G6 senor and are on sensor 15 or so.

If I got a G6 sensor that was reporting off by more than the 20/20 rule that Dexcom uses, I would call Dexcom and get a replacement.

When you put in the G6 sensor where are you putting in the 4 digit number that is on the sensor?
Are you using the Dexcom calcuation on your XDrip+ instance or are you using a different reporting method. I would make sure it matches the Dexcom processing before calling about a sensor not reading correctly.

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Thanks Chris. Yes, I put the 4 digit number in, but am not sure about using the Dexcom calculation…I have been following instructions here both times on how to set up the xDrip+ with the G6. Maybe someone can point to some things to try so that it works as well as the Dexcom app did for me. The reasons why I don’t think it’s the sensor is that I had the exact same issue with the first sensor I used, which was perfectly accurate using the Dexcom app then was off when I switched it over to the xDrip+ app. This time I started right away with xDrip+.

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@docslotnick, what do you think?

@Headlands Try starting your G6 sensor with the Dexcom receiver simultaneously with xDrip+. I have had similar problems with getting my G6 started with my first two sensors, but xDrip+ should pick right up when the receiver starts reading, as long as your xDrip+ is connected to the transmitter

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Unfortunately I don’t have a Dexcom receiver…I only use my smartphone. Possibly a stupid question: Is there a way to do this with the Dexcom app on my phone?

@Headlands Unfortunately, no. Unless they are on two separate phones. The xDrip+ app and Dexcom app can’t be on the same phone.

Make sure in xDrip+ you are using the OB1 collector and native algorithm, both in G5/G6 Debug settings.

Looks like those are set correctly. Well, when my insurance kicks in for the G6 I’ll pick up a receiver so that this doesn’t happen. Thanks for the help!

I’m going to try it with my girlfriend’s cell running the Dexcom app next time I start a new sensor in a couple weeks. Do I start the Dexcom app on her phone first when inserting a new sensor and then start xDrip+ on mine?

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@Headlands Either way. But it will look like xDrip+ is not working during the warm up. The Dexcom app will probably
start giving readings first, then xDrip+ will kick in after 10-15 minutes. Just be patient.

Good luck!

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I have the exact same issue you are describing. I have yet to find a solution. I despise the dexcom app. It forces you to change sensors every 2 weeks. The alarms are awful. The sharing is terrible. Xdrip is better in every way. It worked flawlessly with my g5. So pissed about this.

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Hi docslotnick – I have a question about this process again. Does the smartphone connect to the transmitter via Bluetooth while the warm up process is happening? That’s the only option I’m seeing in the Bluetooth availability on my phone.

@Headlands Yes, during the warm up the transmitter sends a Bluetooth burst every five minutes, just like in a session. But during the warm up the phone doesn’t show numbers, just trend arrows, because the numbers are not accurate while the app is building the algorithm data tables.

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Right, but I mean when you’re starting it on the transmitter and the phone at the same time.

In my as yet limited experience (only been using the G6 since Oct 18) new sensors are flakey. Some work just fine after the 2 hour warm up, some need a lot longer. Like the OP I only use xDrip+

I suspect the Dexcom receiver doesn’t tell the whole truth - its display was a lot smoother than the xDrip+ one when I used both. I can see the transmitter corrections when they occur when using xDrip+; the trace will suddenly duck’n’dive then reset and stabilize.

I haven’t done a detailed analysis of the logs but my impression is that the sensor stablizes over several days then, maybe 15 or so days in, starts to break down eventually resulting in the transmitter detecting sensor errors and stopping delivering readings (it still talks to xDrip+) while it tries to recover.

I just put up with the misbehavior in the first couple of days and try to keep the sensor going for as long as possible. I hate that 2 hour warm up; it feels like being on a liferaft with a hissing noise in the background.

I’ve stopped trying to calibrate; if I think I might need to I check when flat in the range 100-150mg/dl and the result (against a Contour Next-One) always seems to match. Outside that range it doesn’t, but my experience was that if I calibrated outside the 100-150mg/dl range everything went out of whack. I just adapt to the under/over reading outside the G6 sweet spot.

I’m pretty near 100% certain that it doesn’t matter how you start the new sensor; all the real intelligence is in the transmitter.

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@Headlands Sorry, misuderstood. I think you’re asking about the receiver and phone being started at the same time. The receiver and phone (Dexcom app) are communicating during warm up. So does the transmitter and xDrip+. Look at the events log during warm-up and you will see.

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I just completed reading the Doc files of XDrip+, Dexcom G87 and Tandem t:slim, and everything I could find online. ( The critical G6 /XDrip+ information is at : xDrip+ settings — AndroidAPS 3.0 documentation )

  • The receiver does not communicate with the phone app. The receiver and phone each communicate with the transmitter independently over different secure Bluetooth channels.

  • The transmitter is stupid. The communication is all handled by an off the shelf Bluetooth transceiver. The A/D converter’s scaling is adjustable like bass and treble tone controls. All calibration does is give the A/D converter new fixed values to “twist” the knobs".

  • The makers’ docs all say that a receiver must do the calibration. XDrip is by default connected through the G6’s secondary channel and not a “receiver” but a remote display. It has the capability of being connected to the primary channel as a receiver which is why it has controls to do it.

  • How you do any calibration especially an unprompted calibration is important. A calibration should be done through only one device. The sensor itself responds to the calibration and reflects that on its future output. You do not repeat the process on other devices. My guess is that the receiver does the calculation and sends the sensor a new value to use as an offset.

  • If XDrip is connected as a remote display (you can use the Dexcom receiver simultaneously), the G6 wouldn’t be able to respond to a sensor code entered through xDrip. When you jump onto a working sensor session already in progress with a Dexcom receiver you don’t enter a sensor code in XDrip and you don’t start the sensor.

  • Display apps will update on independent schedules different from the receiver controlling the G6. If you had XDrip connected to the G6, and t:connect connected to the T:slim, the one app could be leading the receiver and the other lagging it. That would explain a difference of as much as the delta between tm reioever si ultaneously), hree consecutive measurements.

  • I’ve read posts that say if you enter too many unprompted calibrations the sensor’s ability to adjust can become overwhelmed and the output erratic.

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