Troubleshooting¶

Symptoms you may see while bringing up an SF06 flow meter, their causes and the fix for each.

Start with the error the call returned (sfm::ToString(r.error)): it separates bus problems (BusWrite, BusRead, NoData on every call) from data problems (Crc) and from configuration problems (UnsupportedGas, VariantUnknown).

Nothing answers¶

Symptom	Cause	Fix
Every call returns `BusWrite`, `BusRead` or `NoData`	Wrong address	Check the ADDR strap: open or GND is `0x2A`; scan the bus
	No pull-ups, or SDA and SCL swapped	External pull-ups on both lines; check the connector pin order (SDA is pin 2, SCL pin 5)
	The sensor is still starting	Wait 20 ms after power-up before the first call
	ADDR tied to VDD	Not allowed: tie it to GND or leave it open
`NotInitialized`	The port's `EnsureInitialized()` failed	Your bus set-up (for the ESP32 port: call `Install()` first)

Reads fail¶

Symptom	Cause	Fix
`NoData` on every read	No start command, `Stop()` was sent, or the sensor was reset (IRQn low after a start)	Call `StartContinuous()` again
`NoData` on some reads	Polling faster than results arrive: 2 kHz, or 2 kHz / N with fixed-N averaging	Expected: skip the tick, or read on the IRQn edge
`Crc` now and then	Noise, slow edges, weak pull-ups, long cable	Stronger pull-ups, shorter wires, 100 kHz
`Crc` on every read	The port returns fewer bytes than asked, or reads with a register byte	Fix the port (Porting)

Commands are refused¶

Symptom	Cause	Fix
Identifier, averaging or a new start fails	The sensor is measuring; it takes these only in idle mode	`Stop()` (it waits the 0.5 ms), then the command
`UnsupportedGas`	The variant has no table for the gas (for example CO₂ on an SFM4300-50)	Use a calibrated gas (Gases and part families)
`VariantUnknown`	The gas's start code depends on the family	`ReadProductIdentifier()` in idle mode, or `AssumeVariant()`
`NotSupported` from `SoftReset()`	The port has no `WriteGeneralCallImpl()`	Add it, or power-cycle the sensor
`NotSupported` from averaging or sleep	SFx6000 part	These commands exist only on SF06 parts
`ExitSleep()` returns `BusWrite`	The port cannot send an address-only write (`len == 0`)	Support empty writes in `Write()`

Do not bypass UnsupportedGas with AssumeVariant(): a thermal sensor read with the wrong gas table gives a plausible, systematically wrong flow.

Readings look wrong¶

Symptom	Cause	Fix
The first readings are a few percent off	Warm-up: accuracy is reached about 30 ms after the start	Discard readings for 30 ms after each start
A reading lags a step change	Average-until-read smooths exponentially when you read less often than every 64 ms (status bit 11)	Read at least every 64 ms, or use fixed-N averaging
A constant offset	The sensor is not horizontal, or the line pressure is outside 0.66 bar to 7 bar absolute	Mount it horizontally with the connector up (Hardware)
The temperature differs from the gas temperature	The sensor reports its silicon temperature	Expected; insulate the sensor if you need the gas temperature