Reporting from the Historian

The reports a utility makes

The calculations

Totals

From a totalizer tag in the controller, stored uncompressed, read at the report boundaries: the value at midnight minus the value at the previous midnight, with rollover handled. Never from integrating a stored flow rate, which is compressed and gapped.

Daily minimum, maximum, and average

From the continuous tag over the day, using only good-quality values, with the count of good samples reported beside the result. A daily minimum residual from a day with a six-hour gap is a minimum of eighteen hours and the report says so.

Values at an interval

For compliance tags collected at the required interval: the value at each interval, or the interval marked missing. The historian interpolates by default on many queries; compliance queries ask for the actual sample.

Run hours and starts

From the digital run status: the sum of on durations, and the count of off-to-on transitions, in the period. A state that was on at the boundary is split correctly.

Exceedances

Each interval where a value was above or below a permit limit, with the duration and the peak. Counted, listed, and matched to the alarm journal.

Chemical usage

From day tank levels and deliveries, or from feeder totalizers, with strength corrections where the dose depends on it.

Bad quality and gaps

A report that fills a gap with the last value, with zero, or with an interpolation, without saying so, produces a compliance record that is wrong in a way an inspector can find. The rule is that a gap is reported as a gap: the interval is marked missing, the reason is given where known, a collector outage, a communication loss, an instrument out of service for calibration, and the statistic that depends on it is computed from what remains and labeled with the coverage. The permit usually says what a missing interval means and what must be done; the report follows it.

Building a report once

1. 1

   Write the specification

   Each number on the report: the tag, the calculation, the time window, the quality rule, the units and rounding, and the source of the permit requirement where there is one. This page is the report documentation and it goes with the template.

2. 2

   Build the template

   In the historian reporting tool, a spreadsheet with the historian add-in, or a reporting package, against the specification. Tags by name, not by copying values.

3. 3

   Test against a known period

   Run the report for a past month and compare every number with the previous method or a hand calculation. Differences are explained before the template is trusted.

4. 4

   Schedule it

   Automatic generation on the schedule, to a folder and an email, with the operator review step before anything is submitted.

5. 5

   Version it

   The template is a document under change control. A tag renamed in SCADA breaks it, and the change process catches that.

6. 6

   Archive it

   Every generated report is kept with the period it covers, alongside the calibration records and the data, for the retention period.

Review and sign-off

A compliance report is a statement by the utility. An operator or the operator in charge reads it before submission, checks the numbers that look wrong against the trend, notes the gaps and their reasons, and signs. Automatic generation removes the transcription errors that used to fill these reports; it does not remove the need for someone who understands the plant to look at the result. A report that says the residual was zero for a day because a collector stopped should be caught at review, not at the regulator.