Device parameters (tags)
A tag (parameter) is one named measurement on a device — temperature, voltage, flow_rate. Each device has one or more tags.
When you add or edit a device you define its tags, each with:
- a name (the key the device/gateway publishes),
- optional unit (°C, V, L/min) shown on widgets — prefilled from the measurement you pick, and editable,
- optional scaling — a factor (multiply or divide) and an offset (see below),
- optional min/max for gauges,
- an optional alarm limit — above, below, outside a range or beyond ± — with an early-warning Watch value and a hysteresis (see alert thresholds and Normal, Watch and Alert),
- optional sound alert for threshold notifications (see sound alerts).
Widgets and rules reference a device + tag pair. If you change a tag's name later, re-point any widgets that used it.
Picking a measurement
When you add a tag you pick its measurement from a list grouped by category — Water Quality, Water Level, Soil, Weather and so on. The pick sets the tag's type and prefills its unit; change the unit before saving if your sensor reports in something else. Water Quality carries pH, Turbidity (NTU), Dissolved Oxygen, TDS, Chlorine, Nitrate, COD and BOD (mg/L), Conductivity (µS/cm), ORP (mV) and Salinity (ppt); Water Level has Level and Depth (m). Giving every tag a unit is worth the few seconds: it labels widgets, groups the device chart, and is how a limit reads as Alarms below 4 mg/L instead of below 4.
Scaling: factor (multiply or divide) and offset
Many sensors report a raw number that isn't the real-world value — a Modbus register might hold the reading in hundredths, or an analog input might report a raw count. A factor and an offset convert that raw reading into a real (engineering) value.
Choose the direction with the Multiply / Divide switch:
Multiply: displayed value = raw × factor + offset
Divide: displayed value = raw ÷ factor + offset
- Reading a Modbus datasheet? Vendor docs almost always give a scale factor to divide by — e.g. "the register stores the value ×10" means divide by 10. Just choose Divide and type
10exactly as the datasheet lists it. (You don't need to invert it to0.1yourself — the platform does that internally.) - In Multiply mode the factor can be any positive number — greater than 1 (e.g.
100) or less than 1 (e.g.0.01,0.001). A register that holds hundredths of an amp is either Multiply0.01or Divide100— both give the same result. - The offset is added after scaling — use it for sensor bias or a fixed baseline. Leave it
0if not needed. - The default is Multiply,
factor = 1,offset = 0(the raw value is shown as-is). A live example under the inputs shows exactly how your numbers are applied.
The platform stores the raw reading and applies the factor and offset for display, so you can adjust them later and every chart — past and present — re-scales. Alert thresholds are entered in the displayed (scaled) value, not the raw one — see alert thresholds.
You can change a tag's scaling, its alert threshold or its Watch value at any time from the device's Edit form — no need to delete and re-add the tag. Open the device, find the tag, and use Edit scaling (or Edit threshold). On a device whose alarms are evaluated in the cloud, editing a limit never restarts its gateway.
How tags appear on the device chart
The chart on a device's page draws every tag over the same stretch of time, but it doesn't force them onto one scale:
- Tags with the same unit share a panel, because their values are directly comparable. Two voltages go on one panel, for example.
- Tags with different units, or no unit, get a panel each. A baud rate of 9600 no longer flattens everything else into a line along the bottom.
- On/off tags (a coil, a discrete input, or a tag of type bool) are drawn as a thin strip under the panels, shaded while the tag is ON.
All panels share the time axis, and hovering shows every tag's value at that moment in one tooltip. Giving your tags a unit helps: it's how the chart knows which tags belong together.