Siemens LOGO! 8 Hours Counter Retentivity: Troubleshooting Power-Off Reset

The Siemens LOGO! 8 (6ED1052-1xx08-0BAx / 0BA8 generation) Hours Counter block is widely used for accumulating motor run-time, but engineers frequently report that the retentive checkbox is grayed out in LOGO!Soft Comfort and that the operating-hours total (OT) appears to reset after a power-cycle. This article explains why the box is intentionally disabled, why simulation behaves differently from the physical module, and how to wire the R and RAL inputs so a manual reset does exactly what you intend.

1. Problem Statement

An engineer configures a Hours Counter in LOGO!Soft Comfort V8.x to track the run-time of a motor driven by output Q1. The intent is straightforward: total motor run-time must be retained across panel power-downs for scheduled maintenance, and must only be cleared by an explicit operator action.

Observed symptoms:

• The Retentivity checkbox in the Hours Counter properties dialog is shown selected but greyed out — it cannot be toggled.
• In LOGO!Soft Comfort simulation (online test / simulation mode), the operating-hours total OT resets to 0 h 0 m when the simulation is stopped and restarted, or when the simulated LOGO! is "powered down".
• On the physical LOGO! 8 module, after loading the program, removing power for several minutes, and restoring power, the OT value is still expected to be retained — and usually is. If it is not, the cause is one of the items in §3.

2. Why the Retentivity Bit is Permanently Greyed Out

The Hours Counter function block in LOGO! 8 stores its retentive counter, setpoint, and remaining-time values in a protected region of non-volatile RAM. According to the LOGO! 8 system manual, this region is reserved for blocks whose retentivity cannot meaningfully be disabled because their integrity depends on it.

The Hours Counter is one such block. Retentivity is hard-coded ON in firmware. The UI shows the checkbox as ticked and disabled so that engineers can immediately confirm retention is active — there is no scenario in which it is not. The same applies to the weekly timer, annual timer, and counter blocks whose retentivity is structurally required.

Reference: LOGO! 8 System Manual (6ED1052-1xx08-0BAx).

3. Root Cause: Simulation vs Physical Hardware

The most common source of confusion is the difference between LOGO!Soft Comfort simulation and the physical LOGO! module:

1. LOGO!Soft Comfort simulation runs entirely in a PC's volatile memory. When the simulation is closed, restarted, or when the "power" of the simulated LOGO! is toggled, all process values — including retentive ones — are discarded. This is by design; the simulator has no persistent backing store.
2. Program transfer from LOGO!Soft Comfort to a LOGO! module (Tools → PC → LOGO!) writes a new program image and, like a cold-start, zeroes the operating-hours counter.
3. Physical power-cycle (mains removed and restored) on a real LOGO! 8: the OT value is preserved because the retentive region is backed by the module's battery-buffered / non-volatile RAM. The exact retention time depends on the LOGO! variant — pure 0BA8 base modules use onboard non-volatile storage; LOGO! 8 with text/binary display (0BA8 standard) retain values through power loss indefinitely within device lifetime.

If a field-installed LOGO! 8 genuinely loses the OT value after a mains interruption, the most likely causes are:

4. R Input vs RAL Input — Functional Difference

Every Hours Counter block in LOGO! 8 exposes two reset-related pins in the block diagram:

• R (Reset): When this input receives a positive edge (0 → 1 transition), the block clears its current OT and MN (remaining time) values to zero. The internal retentive counter is reset.
• RAL (Reset All): When this input receives a positive edge, the block resets everything — OT, MN, and also re-initialises the setpoint values OT and MN as configured. The behavior is functionally similar to R for the OT counter, but RAL is reserved for "nuclear reset" use cases such as commissioning or full counter clear-down.

Best-practice wiring is:

1. Leave RAL permanently open (unconnected).
2. Drive R with a single positive-edge impulse from a momentary pushbutton or an HMI "Reset Hours" button. Do not hold R high continuously — a sustained high level will not produce repeated resets, but a positive edge is the documented triggering condition and is easier to reason about.

Looping R and RAL together as a single reset signal is acceptable but unnecessary. The two inputs share the same triggering semantics (positive edge on either resets OT). The distinction matters more in blocks where RAL has a broader scope (e.g., counter blocks where RAL also resets the setpoint).

5. Manual Reset Ladder Logic (LAD) Example

The following LAD snippet implements a one-shot reset for the Hours Counter. I1 is a normally-open pushbutton wired to a digital input. The output of the AND is a single-cycle pulse even if the operator holds the button.

Network 1 — Reset pulse (one-shot)
  I1 (NO) ──┬──[ ]──┐
             │      │
  I1 (NC) ──┴──[/]──┴──( )── M1   ; edge via M1 internal flag

Network 2 — Apply edge to R
  M1 ──────[ ]──( R of Hours Counter B014 )

Network 3 — Motor run drives Hours Counter
  Q1 contact ──[ ]──( EN of Hours Counter B014 ) ; EN = run signal

Edge semantics matter: R only resets on a rising edge. A static 1 on R while the counter is enabled will be ignored on subsequent scans. This is why a one-shot is the cleanest pattern.

6. Accuracy Limitation of the LOGO! Hours Counter

A subtle but operationally important point: the LOGO! Hours Counter only registers complete minutes. Any fractional minute of a run-cycle is silently discarded.

Example: A motor that runs for 59 s every cycle, repeated continuously, will display 0 h 0 m indefinitely. The accumulated 59 s/cycle never rolls over into a counted minute because the block only increments when the internal 1-minute timer elapses with the EN input still high at the moment of rollover.

For duty cycles below 1 minute (e.g., jog modes, short production batches), this causes significant under-reporting. Two mitigation paths exist:

1. Use an Up/Down Counter + a 1-Hz / 0.0167-Hz clock generator to integrate run-time in seconds with finer granularity.
2. Use a mathematical approach — count seconds in an Up/Down Counter and divide by 3600 with integer math, displaying total hours as a separate message text.

7. Improved-Accuracy Ladder Alternative (1-minute display delay)

The following pattern counts full seconds in an Up/Down Counter and rolls them into a separate "hours" counter every 3600 s. Trade-off: the OT display lags by up to 1 hour, but the resolution is 1 s instead of 1 min.

Network 1 — 1-Hz clock generator
  (LOGO! Soft Comfort: "Clock generator" block, period = 1 s)
  Clock_1Hz ──┬──[ ]──┐
              │      │
  Motor_run ──┴──[/]──┴──( CU of Counter C001 )

Network 2 — Reset seconds counter every hour
  Counter C001 (CV = seconds_this_hour, threshold 3600)
  C001.Q ──[ ]──( R of C001 )            ; clear when 3600 reached
  C001.Q ──[ ]──( CU of Counter C002 )   ; +1 hour

Network 3 — Display
  C002.CV ──> Message text "Total run hours: %d" (ANZ block)

This sacrifices 1 minute of update latency (display rolls over at the top of each hour) but eliminates the partial-minute loss issue completely.

8. State-Diagram of the Hours Counter Reset Logic

[ IDLE ]
   |
   | EN rising edge
   v
[ COUNTING ] ---> OT increments every minute
   |
   | R or RAL positive edge
   v
[ RESET ] --> OT := 0, MN := ON
   |
   | next scan
   v
[ IDLE ]

Retentivity: OT persists through power-cycle in all states.
Program transfer: forces transition IDLE (OT := 0).

9. Verifying Retentivity on Physical Hardware

To prove the OT value survives a power-down, perform this procedure on the installed LOGO! 8 module:

1. From the LOGO! display, navigate to the Hours Counter parameter and note the current OT (e.g., 0042 h 17 m).
2. Power off the panel at the mains isolator. Wait at least 30 seconds.
3. Restore mains. Wait for LOGO! to complete its boot cycle (approximately 3–5 s).
4. Re-enter the Hours Counter parameter on the display. The OT value must still read 0042 h 17 m, or higher if the motor ran during the test.
5. If the OT value reads 0000 h 00 m, the program was reloaded between the two readings. Confirm by checking LOGO!'s menu: → Diagnostics → Last program transfer date/time (available on 0BA8.FS4 and later).

For LOGO!Soft Comfort verification on PC: use Tools → PC → LOGO! (or ESC-equivalent on the module) and confirm the OT value via the online monitor before and after a simulated power-down. Remember: the simulator will reset the value, while the hardware will not.

10. Firmware & Variant Considerations

LOGO! 8 (0BA8) uses non-volatile FRAM-style storage and does not depend on a coin-cell battery. Older LOGO! 6 / LOGO! 7 installations retain their OT values only as long as the onboard battery is serviceable; if the battery is dead, the retentive region — including the Hours Counter — is cleared on every power-down. If the application is being migrated from LOGO! 7 to LOGO! 8, this is a common source of "the counter was retentive on the old one, not on the new one" reports, when the actual cause is a depleted backup battery in the older device.

11. Troubleshooting Matrix

12. Frequently Asked Questions