Controlling Hydraulic Proportional Valves with LOGO! 8 and AM2 AQ

Overview: Smooth Hydraulic Lift Control with LOGO! 8

Controlling a single-acting hydraulic cylinder for a lifting application with a Siemens LOGO! 8 (6ED1052 series) requires one piece of hardware that the base module does not natively provide: a true analog output. The base LOGO! 8 modules expose analog inputs (0–10 V on I7/I8 of certain variants) but no analog output. To drive a proportional directional control valve with a 0–10 V command signal, you must add the LOGO! AM2 AQ analog output expansion module.

This article addresses the three questions raised in the source scenario:

1. Which proportional valve interface (0–10 V, 4–20 mA, or PWM) and which valve topology (single-solenoid proportional vs. dual-solenoid / 3-position / 4-way) suits a 220 bar, 80 L/min single-acting cylinder?
2. Is the AM2 AQ module (Siemens part 6ED1055-1MM00-0BA2, "0/4–20 mA, 2 AQ, 0–10 V") sufficient on its own?
3. How do you build a LOGO! program that ramps the analog output from 0 V to 10 V (and back) over a defined period — for example, 5 seconds — to achieve smooth start and stop?

Prerequisites

LOGO! 8 Base Module: Why You Need an Expansion for Analog Output

The LOGO! 8 base module has no analog output channel. The "0–10 V" markings found on the I7/I8 terminals of certain variants (e.g. 6ED1052-1MD08-0BA1, the LOGO! 8 24VCEO with display) are analog inputs only. Those inputs are also configurable as digital inputs and share the same physical terminal with the digital function. There is no terminal pair on the BM that can source a variable DC voltage under program control.

Two expansion paths exist:

1. AM2 AQ — two 0–10 V / 0/4–20 mA outputs, 12-bit, screw terminals, 24 V DC powered. This is the module specified in the source question.
2. LOGO! TDE / 4DO — discrete-only; cannot produce an analog command.

For the application described, the AM2 AQ is the correct and only sensible choice among LOGO! 8 expansions. It is the device referenced in the question ("AM2 AQ expansion module LOGO! 8 DC 24, 0/4–20 mA, 2AQ, 0–10 V").

AM2 AQ Module: Electrical and Signal Specifications

Selecting the Proportional Valve

Interface signal: 0–10 V vs. 4–20 mA vs. PWM

Proportional valves for mobile and industrial hydraulics come in three electrical command flavors:

Recommendation: choose a proportional valve with an integrated amplifier accepting 0–10 V (e.g. the Rexroth 4WRAE10-style direct-operated NG6 proportional valve, Continental VED05MG, or equivalent NG6 / D05 proportional directional valve from Parker's proportional valve portfolio). Then connect AM2 AQ output AQ1 directly to the amplifier's command input.

Valve topology: 1-solenoid vs. 2-solenoid (3-position, 4-way)

For the source scenario — a single-acting cylinder, pump on for raise, gravity-driven lower with pump off, valve closed at rest — the simplest viable topology is:

• 4/3 proportional directional valve, spring-centred (P-T centre, all ports blocked at 0 V), with two solenoids, or
• 4/2 proportional directional valve, spring-offset to tank, single solenoid, with a separate pilot-operated check valve to hold the load.

For a single-acting cylinder, a 2-solenoid 4/3 valve is wasteful (one solenoid controls the unused port). The pragmatic industrial pattern is:

1. Use a single-solenoid proportional throttle valve (or a 4/2 spring-offset proportional valve) on the cylinder port, plus a pilot-operated check valve between pump and cylinder.
2. AM2 AQ drives the proportional throttle: 0 V = full closed (load held by check valve), 10 V = full open (free descent under gravity).
3. Pump is energised through a LOGO! digital output when raising, and a separate pressure-compensated flow path is used when lowering.

If a 2-solenoid valve is already on hand, wire solenoid A to AQ1 (raise) and leave solenoid B unconnected — but verify the spring centre position in the data sheet first. A P-T centred valve is fail-safe: on power loss the cylinder is locked.

Sizing for 80 L/min and 220 bar

At 80 L/min nominal flow and 220 bar system pressure, the proportional valve must be rated for at least 80 L/min at Δp ≈ 10 bar (a typical pressure drop for a Cetop 3 / NG6 / D05 proportional valve to maintain control authority). The reference proportional valves in this class are typically rated 60–100 L/min at the recommended Δp. Verify the specific valve data sheet, paying attention to:

• Maximum operating pressure (must be ≥ 220 bar + 10% margin)
• Nominal flow at the recommended Δp (must be ≥ 80 L/min)
• Hysteresis (≤ 3% recommended for smooth control)
• Step response at the load (determines ramp time selection)

Wiring the AM2 AQ to the Valve Amplifier

1. Power the AM2 AQ from the same 24 V DC supply that feeds the LOGO! BM. Tie all 0 V terminals (BM, AM2 AQ, valve amplifier) to a single star point to avoid ground loops on the analog return.
2. Run a shielded twisted pair (e.g. LiYCY 2 × 0.34 mm²) from AM2 AQ terminals AQ1 (terminal 3) and M (terminal 4) to the proportional valve amplifier's command input (often labelled "+U_cmd" and "GND" or "0 V").
3. Connect the cable shield at the valve amplifier end only; clip the drain wire at the LOGO! end to prevent a ground loop.
4. Provide a 24 V DC enable/PSU to the valve amplifier from the same supply.
5. The proportional valve's load-sense and pilot pressure connections are made on the hydraulic side per the manufacturer's data sheet — these are not electrical concerns of the LOGO!.

Program Design: Generating a Ramped 0–10 V Command

Block choice in LOGO! Soft Comfort

LOGO! Soft Comfort ships an Analog Ramp function block (BF catalog: "Analog Ramp") that is purpose-built for this application. It accepts a start level, an end level, a ramp time, and a digital enable. Alternatively, the Math block combined with a counter and the PI Controller block can produce the same output, but the Analog Ramp block is the simplest and gives a linear profile with the smallest program footprint.

Signal chain

1. Digital input "Raise start" (e.g. I1) — momentary pushbutton, NO, with a sealing contact from a status flag so the LOGO! keeps the ramp running after release.
2. Digital input "Lower start" (e.g. I2) — same pattern.
3. Digital input "Stop / E-Stop" (e.g. I3) — NC, hardwired safety; this should also be wired to a dedicated safety relay that removes 24 V from the pump contactor and from the AM2 AQ output enable line if available.
4. Analog Ramp block configured: SP_start = 0, SP_end = 1000 (full scale 0–10 V is internally scaled to 0–1000 in LOGO!), ramp time = 5 s, ramp up enabled by "Raise start" flag, ramp down enabled by "Lower start" or "Stop" flag.
5. AQ1 output wired to the Analog Ramp's output.
6. Digital output Q1 energises the pump contactor only when AQ1 > 0 (use an analog threshold block, "Analog Comparator", with threshold = 50 — i.e. 5% of full scale).

Sample FBD program (LOGO! Soft Comfort V8.3)

Network 1 — Raise command with seal-in
  I1 ──┐
       ├──[OR]── B001 (RS latch, S=OR, R=Stop/E-Stop)── B001_contact
  B001_contact ──┘

Network 2 — Lower command with seal-in
  I2 ──┐
       ├──[OR]── B002 (RS latch, S=OR, R=Stop/E-Stop)── B002_contact
  B002_contact ──┘

Network 3 — Analog Ramp (block B003)
  Inputs:
    SEL   = B001_contact   (1 = raise, ramp up from 0 to 1000)
    RST   = B002_contact   (1 = lower, ramp down to 0)
    ENA   = NOT(Stop_flag) (1 = enable, 0 = freeze output)
    SP    = 1000           (full-scale setpoint)
    RT    = 5 s            (ramp time)
  Output:
    AQ_raw = 0..1000 ──── AQ1 (AM2 AQ channel 1, 0–10 V mode)

Network 4 — Pump contactor interlock
  B003_out > 50  → B004 (Analog Comparator) ── Q1 (pump contactor)

Network 5 — Stop/E-Stop
  I3 (NC) ── Stop_flag ── (resets B001, B002, enables B003 ENA only when safe)

Set the AM2 AQ channel 1 to 0–10 V mode in the LOGO! Soft Comfort hardware catalog. The internal scale of 0–1000 from the Analog Ramp block maps linearly to 0–10 V at the AQ1 terminal (0 = 0 V, 1000 = 10 V).

Parameter mapping summary

Verification Procedure

1. Bench test (no hydraulic pressure): Connect AQ1 to a multimeter (V DC). Trigger Raise, confirm voltage ramps 0.0 → 10.0 V over 5 s ± 0.1 s, then back to 0.0 V on Stop. Use LOGO!'s on-line monitor to verify the raw value tracks 0 → 1000 in real time.
2. Hydraulic no-load test: With the cylinder disconnected from any load, command a raise and confirm the cylinder extends smoothly without jerking. Repeat for lower.
3. Hydraulic loaded test: Add the rated load. Command lower; verify the descent rate is controllable via AQ1. If the cylinder free-falls at AQ1 = 100, the pilot-operated check valve is bypassing the throttle — re-seat or replace it.
4. E-Stop test: Press E-Stop. The ramp's ENA must drop to 0 (output freezes at its current value), and Q1 must drop. The separate safety relay must also drop 24 V from the pump contactor and from the AM2 AQ supply, forcing AQ1 to 0 V.
5. Power-loss test: Remove 24 V from the LOGO! BM and AM2 AQ simultaneously. The spring-centred valve must lock the cylinder in place. If it does not, add a check valve on the cylinder port.
6. Long-term: Log AQ1 setpoint vs. actual cylinder velocity over 100 cycles and verify no drift; the analog output calibration of the AM2 AQ is stable across temperature to within 0.5% of full scale.

Troubleshooting Matrix

Safety Engineering — Minimum Viable Architecture

Even for a personal/hobby lift, the following layers are non-negotiable:

1. Hardwired E-Stop in the 24 V supply to the AM2 AQ and to the pump contactor — not just a LOGO! input. Use a safety relay (e.g. Pilz PNOZ s5, Sick i10) so a single broken wire or a LOGO! firmware fault cannot keep the pump running.
2. Pressure relief valve set to 110% of maximum working pressure, plumbed directly at the pump outlet.
3. Pilot-operated check valve on the cylinder port for load holding — do not rely on the proportional valve alone.
4. Mechanical stops at top and bottom of travel, plus limit switches wired to the LOGO!'s E-Stop chain.
5. Rupture protection on the cylinder line (per EN 81-20 §9 in the elevator context, and good engineering practice otherwise).
6. LOGO! firmware ≥ V8.3 for the AM2 AQ block-level support and 12-bit analog stability; check the firmware with the LOGO! display (Menu → Diagnostics → Software).

Alternative Architectures and When to Choose Them

• S7-1200 with SM 1232 AQ — if the application grows beyond a hobby lift, the S7-1200 + SM 1232 analog output module gives 13-bit resolution, PID control, and far better diagnostic depth. Same TIA Portal programming environment.
• LOGO! + external PWM driver — only justified if the proportional valve lacks on-board electronics and must be driven with a 1–2 A current command. For a 0–10 V amplifier, this is unnecessary.
• LOGO! + 4–20 mA valve — preferred for cable runs > 10 m or in electrically noisy plants. Switch the AM2 AQ channel 1 to current mode in the device configuration; no program changes needed.

References for Further Engineering (manufacturer documentation, not community material)

• LOGO! 8 system manual (Siemens Support, 6ED1050-1xx08-0BA1)
• LOGO! AM2 AQ (6ED1055-1MM00-0BA2) device manual
• Rexroth 4WRAE direct-operated proportional directional valve (industrial hydraulics catalog)
• Parker proportional valve series
• EN 81-20:2020 — Safety rules for the construction and installation of lifts
• Directive 2014/33/EU (Lifts Directive)
• Directive 2006/42/EC (Machinery Directive)