LOGO! 8 Downtime Capture: Build a Conveyor Data Logger

1. Application Overview

This reference describes a complete downtime-capture application built on a Siemens LOGO! 8.2 logic module (firmware family 0BA8 / FS:02 and later) for a single-vendor conveyor line. The conveyor is fitted with a discrete PNP or NPN sensor that signals product present. When the sensor remains unmade for more than 60 seconds during a scheduled production shift, the LOGO! accumulates the elapsed time, logs it to a micro SD card, and exposes a live web view for management. At the end of each shift the operator removes the SD card and opens the resulting CSV in Microsoft Excel for charting.

The application is intentionally built with stock LOGO! function blocks: weekly timer, on-delay, edge-triggered pulse, counter / hour counter, and the integrated DataLog block. No custom function blocks, scripts, or HMI panels are required, which keeps the engineering footprint small and the validation path auditable for a first-time PLC user.

1.1 Operating Schedule

2. Functional Requirements and I/O Map

Capture the full functional specification in a single I/O map before opening LOGO! Soft Comfort. The table below is the binding document for wiring, programming, and FAT.

3. Hardware Selection and Wiring

3.1 Recommended LOGO! 8.2 Base Module

The DataLog block, integrated Ethernet, and SD card interface are present on the 0BA8 / FS:02 generation. Use one of the following base modules (or their 12V/24V equivalents):

Reference the LOGO! 8 system manual for full ratings, derating, and installation clearances: LOGO! 8 System Manual (Siemens Support, 109751654).

3.2 Sensor Wiring

Use a 3-wire PNP normally-open photoelectric or inductive sensor. The dark-on / light-on mode is set in the sensor; the application uses light-on so the input is high when product is detected.

Wire colours match IEC 60446:

• Brown (BN): +24 V DC to sensor pin 1 / L+
• Blue (BU): 0 V DC to sensor pin 3 / M (and to LOGO! M terminal)
• Black (BK): switched output to LOGO! I1

3.3 SD Card Requirements

Use a micro SD or SD card (with adapter) of 4 GB to 32 GB SDHC capacity formatted as FAT32. SDXC cards (64 GB+) are not supported. Industrial-grade cards (for example Siemens 6ES7648-2BF10-1QA0 or comparable) are recommended in panel-mount installations where vibration or temperature extremes are expected.

4. Software Prerequisites

Download the latest LOGO! Soft Comfort installer and firmware updates from the Siemens Industry Online Support portal: LOGO! Soft Comfort V8.x Documentation.

5. Shift Window Logic (Weekly Timer)

The shift window is implemented with a Weekly Timer block (drag from the Special > Timer palette as Weekly timer). On a 0BA8 module, the block provides up to three independent cams; the LOGO! 8.2 firmware can expose additional cams per block depending on the catalog version. Configure one cam per active day.

5.1 Block B001 — Weekly Timer (Shift Window)

Connect B001.Q directly to M8 (flag SHIFT_OK) so the rest of the program can AND the shift condition with the sensor-debounce result.

5.2 Block B006 — Nightly Reset Pulse

Use a second weekly timer with a single very-short cam to fire at 00:00:00 of each day:

The rising edge of M11 drives the DataLog trigger and the counter reset. The pulse is 60 s wide, which is long enough to be captured reliably by the DataLog block's edge detector.

6. Downtime Detection Filter

The 1–2 s inter-product gap is filtered using an On-Delay block with TA = 60 s. The on-delay is preceded by an Off-Delay of 2 s on the sensor input to debounce the photoelectric / inductive pickup at line edges; this prevents a 50 ms false-low from re-starting the 60 s timer.

6.1 Block Sequence

1. B010 — Off-delay, TA = 00:00:02 (sensor debounce). Input: I1. Output: M12.
2. B002 — On-delay, TA = 00:01:00 (60 s). Input: M12. Output: M13.
3. B011 — AND with shift window. Inputs: M13 AND M8. Output: M9 (DT_ACTIVE).

Logic expression for DT_ACTIVE:

DT_ACTIVE = SHIFT_OK · ¬(sensor ON for < 60 s)

Equivalently, expressed with the block variables:

M9 = M8 AND (NOT M12_LATCH) where M12_LATCH is the 60-second-on-delayed negation of the debounced sensor

6.2 Why an On-Delay, Not a Pulse Generator

A pulse generator would toggle every cycle regardless of whether product ever returned. The on-delay only sets the output high after the sensor has been continuously low for the threshold, which matches the spec: "start counting only when the sensor is not made for about 1 minute."

7. Downtime Accumulator

Two implementation options are available; the choice depends on which value the DataLog block writes.

7.1 Option A — Hour Counter (recommended for minute resolution)

The Hour counter block (B008) increments an internal MM:SS register whenever its EN input is high. With EN = DT_ACTIVE (M9) the counter records the wall-clock duration of every downtime event inside the shift window. Reset it via R = M11 (DT_RESET_P).

7.2 Option B — Up Counter of 1-Minute Pulses (integer minutes)

If management prefers a clean integer minutes value, drive a 1-minute pulse generator and feed an up-counter.

The counter value is an integer minute count for the current shift. The conversion from MM:SS in option A to integer minutes is:

downtime_minutes = floor(MM·60 + SS) ÷ 60

Implement this in Excel with the formula =INT((HOUR(A1)*60+MINUTE(A1)+SECOND(A1)/60)) applied to the imported timestamp field, or do the floor in the LOGO! by using the integer counter option directly.

8. DataLog Configuration

The DataLog block is the bridge to Excel. Place it on the diagram and configure columns that match the variable memory addresses of the two accumulators above.

8.1 Block B004 — DataLog

Trigger the block on the rising edge of M11 (the 00:00 nightly pulse). The block writes one row to /datalog.csv on the SD card. File-system path and naming are firmware-dependent; the canonical default is the SD card root with file name downtime.csv, but verify in the DataLog block properties dialog.

8.2 SD Card File Format

Files are plain CSV with ; or , separator depending on the LOGO! configuration (default separator: ; to suit European Excel locales). The file header is one row; subsequent rows are the daily records.

Timestamp;DayOfWeek;DowntimeMin;DowntimeHM;ShiftOK
2024-03-04 00:00:01;1;37;0:37:00;0
2024-03-05 00:00:01;2;12;0:12:00;0

Open the file in Excel with Data > From Text/CSV and select the matching separator. Excel will then expose the columns as a structured table.

9. Web Server for Live Monitoring

The LOGO! 8.2 firmware exposes an extended web server that displays variable values in real time. Use it as the management "dashboard" for the current shift.

1. Connect a Cat5e patch cable from the LOGO! Ethernet port to a managed switch on the company network.
2. From LOGO! Soft Comfort, set the LOGO! IP (default 192.168.0.10) or enable DHCP. Verify with ping from a PC.
3. Open the variable list in the Tools > Define Web Server Variables menu and mark the addresses VW0, M8, M9 as visible.
4. Open a browser to http://192.168.0.10 (or the assigned IP). The default page shows the LOGO! status, current variables, and a tag for each selected VM area.

10. Excel Export and Visualization

End-of-shift procedure for the operator:

1. Power the LOGO! off (recommended but not required; the SD card can be hot-removed in most firmware versions).
2. Open the SD card slot cover, depress the card, and remove it.
3. Insert the card into a PC.
4. Copy downtime.csv to a folder named with the shift date, for example Y:\OEE\2024-03-04\downtime.csv.
5. Open in Excel via Data > From Text/CSV.

10.1 Recommended Excel Layout

10.2 Recommended Charts

• Daily downtime bar chart: insert a clustered column chart of Date vs DowntimeMin. Right-click > Add Data Labels.
• OEE trend line: insert a line chart of Date vs OEE %. Use a secondary axis if combining with the bar chart.
• Threshold conditional formatting: apply a red fill where DowntimeMin > 60 to flag days above the alert threshold.

11. Simulation, Commissioning and Verification

11.1 Offline Simulation in LOGO! Soft Comfort

1. From the menu Tools > Simulation (or press F3) enter simulation mode.
2. Open the I/O Status dialog. Force I1 = 1, force the system clock to 07:00 on a Monday.
3. Confirm that M8 (SHIFT_OK) goes high within 1 s of the clock crossing 07:00.
4. Force I1 = 0 and let the simulation run for 65 simulated seconds. Confirm M9 (DT_ACTIVE) goes high at 60 s and that VW0 (or the hour counter) starts incrementing.
5. Force I1 = 1 again. Confirm M9 drops immediately (the on-delay does not require a falling-edge reset).
6. Move the clock past 00:00 of the next day. Confirm M11 pulses, the DataLog block records one row, and the counter resets to zero.

11.2 On-Site Verification Checklist

12. Troubleshooting Matrix

12.1 Common Configuration Pitfalls

• Off-time 24:00 vs 00:00: depending on firmware, the weekly timer cam may interpret 24:00 as 00:00 of the next day. If the cam appears to never turn on, set Off = 23:59 and add a pulse generator for the reset.
• Retain not enabled: if the LOGO! loses power mid-shift, the counter value is lost. Enable Retain on the counter and on the DataLog row pointer to survive power cycles of up to ~80 hours (LOGO! has a super-cap that retains RAM for short outages; for longer outages the SD card is the source of truth).
• DataLog trigger race: if the trigger edge and a process variable change occur in the same LOGO! scan, the recorded value can be the new value, not the previous shift's value. Add a 1 s delay between the shift-end edge and the DataLog trigger to give the counter a final cycle to settle.

13. Field Commissioning Notes and Edge Cases

13.1 Long-Weekend Behaviour

Because the cam mask only includes Mon–Fri, no rows are written on Saturday or Sunday. The CSV therefore has a one-row gap from Friday 00:00 to Monday 00:00; this is intentional and reflects production, not a fault.

13.2 Shift Overrun Across Midnight

If a shift ever runs past 00:00 (for example a Friday that ends at 02:00 Saturday), the current program will stop counting at 00:00 and reset the counter. To support an overrun, add a second weekly timer covering 00:00 – 02:00 Sat and OR its output into M8 with a separate counter (M_Sat) so the data is segregated by calendar day.

13.3 Sensor Power Loss as Downtime

If the sensor loses power, its PNP output is undefined. With light-on wiring, a powered-down sensor typically presents a low (0) to I1, which the application will correctly classify as downtime after the 60 s filter. Verify with a controlled test: disconnect the sensor wire and observe M9 after 60 s.

13.4 Alternate Display Options

The optional LOGO! TDE text display (6ED1055-4MH08-0BA0) can show the current downtime in plain text on the conveyor, useful for line operators. The text-display page is configured in LOGO! Soft Comfort with the message text block.

13.5 Migrating to a LOGO! 8.3 or Later

LOGO! 8.3 (FS:03) adds MQTT publish directly from the variable table, removing the need for SD card retrieval in a networked plant. The program above is forward-compatible: the DataLog block can be retained as a backup, and a new MQTT client block can be added that publishes the same VW0 value once per minute.

14. Bill of Materials