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What is a process historian in a plant?

A process historian is a database that stores readings from plant equipment over time, such as flows, levels, pressures and temperatures. Engineers use it to spot trends, trace the cause of a fault and report on a shift. PI System (formerly OSIsoft PI) is a well-known example.

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Glossary

Process historian

In plain English, with what it means for alert texts.

Illustration of Process historian.

How a process historian works

Each stored value is a tag reading with a time stamp, often taken from a programmable logic controller in the field. A tag is the name for one measured point, like the level in Tank 12.

The historian squeezes years of readings into little space, so a trend from last March loads in moments. Operators rarely open it while an alarm is live. They use it the next morning to see what led up to the fault.

Can a process historian send alerts?

Yes, through the tools around it. Alarm tools that read historian data, such as TopView, can send an email when a value crosses a limit.

That is handy for slow problems a SCADA alarm may not catch. Think of a pressure that creeps up over hours as a cold snap sets in.

A historian alarm as a text

A tank vent alarm at a process plant, built on historian data, emailed by the alarm tool and texted to the shift lead.

  • Tank vent pressure alarm: Welco: [Tank 12] Vent pressure HIGH, check system at 8:19 AM. Reply STOP to opt out.

A phone showing these alert texts: Tank vent pressure alarm, "Welco: [Tank 12] Vent pressure HIGH, check system at 8:19 AM. Reply STOP to opt out."

Process historian vs SCADA

SCADA shows what is happening now and raises alarms. A historian keeps the record, so you can look back at last night or last year.

Many plants run both, with SCADA feeding the historian. Plant and texting words like these fill our alarm and texting glossary.

What a historian means for your alert texts

Welco works with PI System and TopView today. Point the alarm email at your Welco address, then use alert rules to choose who gets each tag.

Setup notes live on the PI and historian alarms page. Try it first in test mode, which logs the text without sending it or using credits.

Frequently asked questions

Is a process historian the same as a database?

It is a database built for one job: lots of time-stamped readings, stored compactly and read back as trends. A general database can store the same data, but it is usually slower for plant trends.

Do I need a historian to get alarm texts?

No. Most alarm texts come straight from SCADA, an HMI or a monitoring tool. A historian helps when you want alerts on slow trends that a live alarm misses.

Which alarms from a historian are worth texting?

The ones someone must act on before morning, such as a level or pressure that keeps rising. Send daily reports and slow drifts to email instead, and keep texts for action.

What is the difference between a tag and a point?

Usually nothing. Both name one measured value, such as a tank level. Some systems say tag, others say point, and a few use both for slightly different things.

Send historian limit alarms to the right phone

Point the alarm email at Welco and choose who gets each tag.

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