Configuring APL TotalL Operating Modes: Integrator vs Summer in PCS 7

In SIMATIC PCS 7 Advanced Process Library (APL), the totalizer block TotalL (FB1906) operates in two mutually exclusive mathematical modes controlled by parameter Mode (or Feature.bit6 and Feature.bit7): Continuous Integrator mode (Mode = 1, Feature.bit6 = 1) and Continuous Summer mode (Mode = 2, Feature.bit7 = 1). In Continuous Integrator mode, the block integrates a continuous flow rate connected to In.Value over time using integration time TI and sampling time SampleTime. In Continuous Summer mode, the block increments its output by discrete quantities arriving on Incr.Value each execution cycle while ignoring In.Value. Configuring Summer mode while connecting a flow rate causes the total to either stall or explode in value.

Operating Modes and Mathematical Algorithms in TotalL

Totalizing fluid volume, mass flow, or discrete production counts is a foundational requirement in process automation. In the SIMATIC PCS 7 Advanced Process Library, the standard totalizing function is provided by TotalL (FB1906).

A common engineering mistake occurs when an engineer configures TotalL to calculate cumulative volume from an analog flow transmitter (such as 0–100 m³/h), but the output remains at zero or calculates wildly inaccurate values. This fault occurs because TotalL supports two fundamentally different calculation principles:

Continuous Integrator: Designed for continuous time-dependent rates (e.g., liters/second, m³/hour, kg/minute).
Continuous Summer: Designed for pre-calculated discrete batch pulse increments or batch packet weights (e.g., adding 5 kg each time a weigh hopper dumps).

Attempting to feed a continuous rate into the summer input or configuring summer mode while connecting to In.Value causes complete calculation failure.

Continuous Integrator Mode Configuration (Mode = 1)

When totalizing continuous flow rates from analog instruments, TotalL must be parameterized as a Continuous Integrator:

Operating Mode Selection: Set Mode = 1 (or configure Feature.bit6 = 1 and Feature.bit7 = 0).
Input Connection: Connect the analog process value structure (PV_Out from Pcs7AnIn) to TotalL.In.
Time Base Configuration (TI): Parameterize the integration reference time TI to match the engineering unit of the flow rate:
Flow in units per second: TI = 1.0 s
Flow in units per minute: TI = 60.0 s
Flow in units per hour (e.g., m³/h): TI = 3600.0 s
Algorithm: The block evaluates trapezoidal integration across execution cycles:
$$Out.Value_n = Out.Value_{n-1} + \frac{SampleTime}{TI} \cdot \frac{In.Value_n + In.Value_{n-1}}{2}$$
Because SampleTime is automatically injected by the CFC compiler based on the cyclic interrupt OB (e.g., 0.1 s in OB35), the totalizer tracks exact cumulative volume.

Continuous Summer Mode Configuration (Mode = 2)

When the upstream instrumentation or logic delivers discrete batch increments rather than a continuous rate, TotalL operates as a Continuous Summer:

Operating Mode Selection: Set Mode = 2 (or configure Feature.bit6 = 0 and Feature.bit7 = 1).
Input Connection: Connect the discrete increment quantity to TotalL.Incr. Input In is completely ignored in this mode.
Algorithm:
$$Out.Value_n = Out.Value_{n-1} + Incr.Value_n$$
Operational Failure Mode: If an engineer mistakenly wires a continuous flow rate of 100 m³/h to Incr while in Summer mode, the block adds 100 to the accumulator every 100 milliseconds. In just one second, the accumulator increases by 1,000 m³, rapidly overflowing the totalizer.

Diagnostic Parameter Table and Feature Bits

The following matrix outlines the parameter settings and signal routing for TotalL:

ParameterData TypeIntegrator Mode (Mode = 1)Summer Mode (Mode = 2)DescriptionFeature.bit6BOOL1 (True)0 (False)Activate Continuous Integrator modeFeature.bit7BOOL0 (False)1 (True)Activate Continuous Summer modeInSTRUCT (AnaVal)Connect flow rate (m³/h, kg/s)Unused (Ignored by block)Continuous rate analog inputIncrSTRUCT (AnaVal)Unused (Ignored by block)Connect increment packetDiscrete increment addition inputTITIME / REALSet to 1s, 60s, or 3600sUnusedTime reference unit for integrationResetBOOLAssert to zero outputAssert to zero outputResets Out.Value to 0.0 or Preset

Both modes support positive and negative flow tracking, pulse generation upon reaching batch thresholds, and automatic high/low limit warnings.

Verification

To verify totalizer operation in the engineering environment:
1. In CFC, open the chart containing TotalL online in test mode.
2. Verify that for an hourly flow rate of 3600 m³/h with TI = 3600.0s, the accumulator Out.Value increments by exactly 1.0 m³ every second.
3. Assert the reset command via RstLi or the WinCC faceplate; verify that Out.Value resets to zero cleanly.
4. Verify that signal status ST of Out reflects the worst quality code between In.ST and internal memory.

Limitations and Operational Precautions

Never place TotalL in an OB task with unpredictable cycle times. Accurate integration requires deterministic execution; always place TotalL in a fixed cyclic interrupt task (OB32–OB38) matching the upstream analog channel driver. If totalizing flow over extended months or years, monitor IEEE 754 floating point resolution loss: when Out.Value becomes extremely large compared to fractional cycle increments, single-precision REAL addition loses precision. Implement periodic resets or double-precision accumulation.

Engineer FAQ

Why did my totalizer stay at zero when I connected my flow rate to In?

Your block had Feature.bit6 = 0 and Feature.bit7 = 1 (Summer mode). In Summer mode, In is completely ignored; the block only evaluates Incr.

What should TI be set to if my flow meter outputs gallons per minute (GPM)?

Set TI = 60.0 seconds. This scales the per-second cycle time of the controller to minutes.

Can TotalL totalize backward/reverse flow?

Yes. If the flow transmitter outputs negative flow rates, TotalL will integrate the negative value, decreasing the totalizer accumulator accordingly.