[{"data":1,"prerenderedAt":164},["ShallowReactive",2],{"doc-\u002Ftroubleshooting\u002Fwrong-readings":3},{"id":4,"title":5,"body":6,"description":154,"edit":155,"extension":156,"meta":157,"navigation":158,"path":159,"seo":160,"stem":161,"vertical":155,"weight":162,"__hash__":163},"content\u002Ftroubleshooting\u002Fwrong-readings.md","Wrong readings",{"type":7,"value":8,"toc":142},"minimark",[9,13,18,26,32,48,51,55,58,62,69,72,76,79,87,91,94,105,109,112,116,119,135],[10,11,12],"p",{},"\"Wrong readings\" almost never means the sensor is lying. Modern SHT3x\nand BME280 chips are accurate to ± 0.4 °C and ± 2 % RH straight off the\nreel. What is wrong is usually where the probe is.",[14,15,17],"h2",{"id":16},"_1-is-it-the-probe-placement","1 · Is it the probe placement?",[10,19,20,21,25],{},"The single most common report on the helpdesk:\n",[22,23,24],"em",{},"\"the fridge is set to +4 °C but OpenSense says +1 °C\"",".",[27,28],"stoplight",{"alarm":29,"ok":30,"warn":31},"Probe on the evaporator surface — measuring the coldest metal in the box, not the food","Probe in the air mid-cabinet, mid-height, away from evaporator","Probe taped to a wall — measuring wall temp, not air",[10,33,34,35,39,40,43,44,47],{},"Cold air sinks. Hot air rises. If your probe is at the ",[36,37,38],"strong",{},"bottom"," of a\nwalk-in fridge, it reads colder than the food on the top shelf. If your\nprobe is ",[36,41,42],{},"near the evaporator",", it reads −2 °C while the door is open\nand food on shelf 3 is at +9 °C. Move the probe to the ",[36,45,46],{},"warmest"," stored\nitem and trust the reading.",[10,49,50],{},"For a display chiller with two shelves, the upper shelf is warmer than\nthe lower one by 2–4 °C. For a chest freezer, the top is warmer than the\nbottom by 3–6 °C.",[14,52,54],{"id":53},"_2-did-someone-tape-the-sensor-to-a-cold-surface","2 · Did someone tape the sensor to a cold surface?",[10,56,57],{},"The Shelly H&T's plastic shell conducts heat slowly but its mounting\nmagnet conducts well. If it is mag-mounted to the steel rail of the\nevaporator coil, the reading drifts toward the rail temperature, not the\nair. Re-mount with Velcro on a non-conducting surface (plastic shelf,\nthe door's inside skin, the underside of a wire shelf).",[14,59,61],{"id":60},"_3-is-the-cadence-the-problem","3 · Is the cadence the problem?",[10,63,64,65,68],{},"If readings appear to ",[36,66,67],{},"lag"," the real temperature — door opened, you\nexpect a spike, you do not see one for two minutes — the cadence is too\nslow. Default is 60 s on Shelly, configurable up to 30 s. For HACCP set\n60 s. For monitoring door-open events, set 30 s.",[10,70,71],{},"LoRaWAN devices have a minimum cadence of 5 minutes in EU868 due to\nduty-cycle limits; do not buy LoRaWAN for door-event monitoring.",[14,73,75],{"id":74},"_4-is-the-value-drifting","4 · Is the value drifting?",[10,77,78],{},"If readings track a real-world reference at first and then slowly drift\n(e.g. one degree per month), the chip is contaminated. Common cause:\nvolatile solvents in the room (cleaning sprays, perfume) hit the\npolymer membrane on the humidity sensor and shift its zero point.\nSensirion SHT3x can be rebaked: leave the sensor at 60 °C in dry air\nfor 24 h; recovery is usually 80 %.",[10,80,81,82,86],{},"If you cannot bake or do not have time, calibrate-out the drift in the\nchannel's ",[83,84,85],"code",{},"offset"," field. Audit-trail-safe: the offset is recorded as a\nconfiguration change with a timestamp.",[14,88,90],{"id":89},"_5-is-it-the-wrong-sensor-entirely","5 · Is it the wrong sensor entirely?",[10,92,93],{},"A surprisingly common scenario: someone bought a \"Shelly H&T\" that turned\nout to be the older Gen1 unit with a different chip (HDC1080 or DHT22 in\nsome counterfeits). Both are factor-of-2 worse on humidity. Symptom: RH\nreading is high, the room actually feels dry.",[10,95,96,97,100,101,104],{},"Check the device's ",[83,98,99],{},"Device info"," page: it lists the chip model. If the\nchip is ",[36,102,103],{},"not"," an SHT3x, replace the unit.",[14,106,108],{"id":107},"_6-is-it-the-rule-not-the-reading","6 · Is it the rule, not the reading?",[10,110,111],{},"A rare but worth-it check: the channel's operating range may have been\nedited to a narrower band, so the same in-bounds reading is now\nconsidered \"out\". Look at the channel history; the right panel shows the\nlast 10 changes to thresholds.",[14,113,115],{"id":114},"when-the-reading-really-is-wrong","When the reading really is wrong",[10,117,118],{},"In the rare case that the sensor itself is faulty:",[120,121,122,126,129,132],"ul",{},[123,124,125],"li",{},"Shelly: shrug, replace. They are €30 retail and the warranty path is\nAmazon's, not ours.",[123,127,128],{},"Aqara: refresh battery, repair to gateway. Has been observed to recover\nafter a deep-discharge and one pairing cycle.",[123,130,131],{},"Efento: contact Efento's support — these are €100 sensors and the\nvendor is responsive.",[123,133,134],{},"DIY ESP32: re-solder the BME280 connections, check the I²C pull-ups\n(the breakout boards have them but the bare chip does not).",[10,136,137,138,141],{},"For HACCP compliance: if the reading was wrong ",[36,139,140],{},"and"," an alarm was\nissued, leave the alarm in the audit trail. Add a free-text note\nexplaining the diagnosis and the corrective action. Auditors prefer this\nto a clean log that you \"edited\".",{"title":143,"searchDepth":144,"depth":144,"links":145},"",3,[146,148,149,150,151,152,153],{"id":16,"depth":147,"text":17},2,{"id":53,"depth":147,"text":54},{"id":60,"depth":147,"text":61},{"id":74,"depth":147,"text":75},{"id":89,"depth":147,"text":90},{"id":107,"depth":147,"text":108},{"id":114,"depth":147,"text":115},"Plausible-but-wrong values — physics, not software",null,"md",{},true,"\u002Ftroubleshooting\u002Fwrong-readings",{"title":5,"description":154},"troubleshooting\u002Fwrong-readings",420,"CWzKio19Uz8wkVtsNR9Kw6thDMTW1sz4VZHAjQpy2U4",1779022955343]