Define the OPC Scaling Requirement
The required engineering range is 0–100% for a level value received through OPC. The available evidence confirms that the Modbus connection exposes a multiplier, but it does not identify an equivalent setting in the OPC connection. It also does not identify the OPC client, OPC server, controller, tag data type, or raw input range, so no product-specific parameter can be specified.
Calculate the Normalized Level
Obtain the raw value at the known empty and full conditions. Then apply linear scaling, assuming the level measurement is linear and the two endpoints are valid:
LevelPercent = ((RawValue - RawAtEmpty) / (RawAtFull - RawAtEmpty)) * 100Do not replace the endpoint values with guessed limits. Also prevent division by zero by verifying that RawAtFull differs from RawAtEmpty.
Select Where to Apply Scaling
| Location | Use when | Required check |
|---|---|---|
| OPC configuration | The specific OPC client or server provides scaling for the data point | Confirm whether the setting changes the published value or only its display |
| Controller or source system | No suitable OPC scaling field is available | Publish a separate normalized value without overwriting a raw value needed elsewhere |
| Application expression | The consuming application supports arithmetic expressions | Confirm the expression uses the intended raw tag and floating-point arithmetic |
A Modbus multiplier and an OPC data-point configuration are not proven to have matching options. Inspect the actual OPC product configuration before assuming that a multiplier is unavailable.
Configure and Verify the Result
- Identify the OPC tag and record its value at the known empty condition.
- Record the value at the known full condition.
- Apply the linear formula in the available OPC, controller, or application layer.
- Verify that empty produces 0%, full produces 100%, and an intermediate physical level produces a proportional value.
- Confirm that the displayed percentage changes in the correct direction. If it is reversed, recheck which measured endpoint was assigned as empty and full.
FAQ
How do I scale an OPC level tag to 0–100%?
Measure the raw values at empty and full, then calculate ((RawValue - RawAtEmpty) / (RawAtFull - RawAtEmpty)) * 100.
Why can’t I find the Modbus multiplier in my OPC connection?
The evidence does not establish that the OPC product exposes the same multiplier option. Check whether scaling exists in the OPC configuration; otherwise apply it in the controller or consuming application.
How do I verify OPC level normalization?
Confirm that the known empty condition reads 0%, the known full condition reads 100%, and an intermediate level changes proportionally in the correct direction.
