You’re staring at a value that spiked an hour ago and now everyone wants to know why. You’ve got the raw data, but without a visual trend you’re piecing together a timeline from memory and log files. Sound familiar?
For automation engineers and maintenance technicians, this is a daily friction point. OPC data flows constantly, but making sense of it across multiple tags, servers, and time windows usually means stitching together several tools or leaning on a historian that may or may not be configured correctly.
OPC Expert changes that. Its built-in trending engine lets you go from “I see a value” to “I see what that value has been doing over time” in a single right-click, with no extra tools, no historian required, and no installation.
Here’s how it works.
Starting a Trend: One Right-Click Away
Once you’ve connected OPC Expert to your OPC server and subscribed to the tags you need, trending is immediate.
To trend a single item:
- In the Realtime Data panel, locate the item you want to trend.
- Right-click the item.
- Select Trend from the context menu.
OPC Expert opens a Trend window and immediately begins plotting live values. There’s no configuration wizard, no tag mapping, no template to fill out. The trend starts streaming the moment you click.
Note: Items from different OPC servers, including servers on different remote computers, can be selected and trended together in the same step. Select multiple items using Ctrl+Click, then right-click and choose Trend.
Trending Multiple Items Simultaneously
The real diagnostic power comes when you’re tracking relationships between tags: flow against pressure, level against current, setpoint against actual.
OPC Expert gives you two ways to build a multi-item trend:
| Method | How to Do It | Best For |
|---|---|---|
| Multi-select before trending | Ctrl+Click each item in the data panel, then right-click and select Trend | Starting fresh with a group of related tags |
| Drag and drop onto an existing trend | Drag an item from the data panel and drop it onto an open Trend window | Adding a tag to a trend already in progress |
Both approaches load all selected items into a shared trend view, with each tag assigned a distinct color and its own Y-axis. Real-time values update continuously in the data table below the chart.
Tip: Running Multiple Trend Windows
You’re not limited to one Trend window. Open as many as you need, and each one tracks its own set of items independently. This is particularly useful when you want to compare two groups of tags side by side without overlapping them on a single chart.
Navigating Time: Real-Time and Historical Data in One View
This is where OPC Expert earns its place in the troubleshooting workflow. The same Trend window handles both live streaming data and historical playback.
To move between real-time and historical:
- Drag the scrollbar to the left to step back in time, pausing live updates so you can examine what happened.
- Drag the scrollbar back to the right and live updates resume automatically.
You don’t switch modes, toggle a historical query, or reconnect to a different data source. The transition is seamless, and OPC Expert handles it transparently whether you’re connected via OPC DA for real-time data or OPC HDA for historian access.
| Scroll Position | Behavior |
|---|---|
| Far right | Live streaming; trend updates continuously |
| Left of live | Historical playback; updates paused |
| Return to right | Live streaming resumes automatically |
No Historian? No Problem.
If your facility doesn’t have a process historian in place, OPC Expert includes a built-in Historian that captures real-time data and archives it to long-term storage automatically. You get historical trending capability without standing up a separate historian system.
Using the Data Cursor
When you need the exact value at a specific point in time rather than a visual approximation, the data cursor gives you precision.
Click and hold anywhere on the trend chart to drop the cursor. OPC Expert displays:
- The exact timestamp at the cursor position
- The value of every trended item at that moment, listed in the data table
This is especially useful when you’re correlating events: “What was the flow rate at exactly the moment the pressure spike occurred?”
![Screenshot: opc-trend-4.png – Trend window with cursor active, showing exact values (62.96, 29.23, 58.40) annotated directly on the chart, callouts: “Cursor indicates trend values at a specific time” and “Zoom in to specific time periods”]
The Selected Time column in the data table updates dynamically as you move the cursor, giving you a live readout of every tag value at that position on the timeline.
Zooming In and Out
When you’ve identified a region of interest, zoom in to examine it in detail.
To zoom in:
- Click and drag to the right across the area of interest. OPC Expert applies animated zoom so you can track which window you’re entering.
To zoom out:
- Click and drag to the left, or use the Zoom Out menu option in the Trend toolbar.
Animated zooming isn’t just cosmetic. It gives you spatial context as the view changes, so you don’t lose track of where you are on the timeline.
Normalizing Scales for Cross-Tag Comparison
Comparing tags with very different units and value ranges is difficult when each one has its own Y-axis. A flow value in the tens of thousands and a pressure value between 0 and 1 will never tell you much on separate scales.
OPC Expert’s Auto Size Axis function normalizes all trended items to the same visual scale, regardless of engineering units. This lets you compare shape and timing across signals that would otherwise be impossible to overlay meaningfully.
To normalize the view:
- Click Auto Size Axis in the Trend window toolbar.
All items shift to a common visual scale, making it straightforward to spot correlated movements, phase shifts, or anomalies that only become visible when the data is visually aligned.
Saving and Restoring Trend Views
If you’ve built a trend configuration your team will return to regularly, covering specific tags, windows, and layouts, you don’t have to rebuild it each time. OPC Expert lets you save the current view to a file, and on the next session it restores automatically. After a reboot, operators can be up and trending immediately without reconfiguring anything.
This is particularly valuable for shift handovers and for control room operators who need consistent monitoring views at startup.
| Feature | What It Does |
|---|---|
| Single-item trend | Right-click any subscribed item and select Trend |
| Multi-item trend | Ctrl+select multiple items, then right-click and select Trend |
| Drag-and-drop add | Drop any item onto an existing Trend window to add it |
| Multiple Trend windows | Open as many windows as needed, each tracking independent tag sets |
| Historical scrollback | Drag scrollbar left to step back in time; returns to live automatically |
| OPC DA / HDA support | Real-time trending via OPC DA; historian access via OPC HDA |
| Built-in Historian | Captures and archives real-time data when no external historian exists |
| Data cursor | Click on chart to see exact values for all tags at any timestamp |
| Zoom in / Zoom out | Drag right to zoom in with animation; drag left or use menu to zoom out |
| Auto Size Axis | Normalizes all tag Y-axes to a common visual scale for comparison |
| Save / Restore view | Saves current trend configuration; auto-restores on next launch |
| REST API | Access trends from any web-enabled device or platform |
| No installation required | Runs immediately on any computer; no registry changes |
Putting It to Work
Think back to that mystery spike at the top of this article. Subscribe to your tags, right-click, and you’re looking at a live chart. Scroll back, drop a cursor on the anomaly, and you have the precise values at the precise moment. Add the adjacent tags to the same window, normalize the axes, and the correlation either appears or it doesn’t.
No historian provisioning. No multi-tool workflow. No installation on a protected production machine.
Download OPC Expert at opcexpert.com and run a trend on your live OPC data today.