Wiring SM 332 6ES7332-5HF00-0AB0 Analog Output Power

Overview

The Siemens SM 332 analog output module with order number 6ES7332-5HF00-0AB0 is an 8-channel output module for the SIMATIC S7-300 family. It generates precisely controlled analog signals (voltage or current) to drive proportional valves, variable-speed drive references, positioner controllers, chart recorders, and indicator lamps. Each of the eight channels can be independently configured for voltage (±10 V, 0–10 V, 1–5 V) or current (0–20 mA, 4–20 mA, ±20 mA) output, with 11-bit plus sign resolution (12-bit) and a typical conversion time of 0.8 ms per channel.

Unlike the digital SM 322 sibling module (which is backplane powered for its outputs), the SM 332 must be wired to an external 24 V DC source on the front connector. The 40-pin front connector is split into two functionally independent groups of four channels each, and each group requires its own 24 V / 0 V supply pair. Failing to connect the supply pair for an in-use group is the most common reason a freshly installed SM 332 reports zero output on every channel of that group.

Module Identification and Variants

SM 332 modules are identified by an MLFB (Maschinenlesbare Fabrikate-Bezeichnung = machine-readable product designation) of the form 6ES7332-5HF00-0AB0. The first block locates the product group:

• 6ES7 – SIMATIC S7 spare part / module
• 332 – Analog output (SM = Signal Module family)
• 5 – Function class (5 = standard analog)
• HF00 – Variant (8 AO, 11/12-bit, electrically isolated between channel and backplane, group-isolated outputs)
• 0AB0 – Hardware revision / release state

The 6ES7332-5HF00-0AB0 ships with:

• 8 analog output channels in two groups of 4
• Resolution: 11 bits + sign (12-bit) bipolar, 12-bit unipolar
• Output ranges per channel: ±10 V, 0–10 V, 1–5 V, 0–20 mA, 4–20 mA, ±20 mA
• Galvanic isolation: between backplane and outputs (500 V DC), between the two output groups (500 V DC)
• Diagnostic LED: SF (group fault), one per group (the module front shows LEDs for group A and group B faults)
• Front connector: 40-pin screw-type (6ES7392-1AM00-0AA0) or spring-type (6ES7392-1BM01-0AA0)

For the official specification sheet, see the Siemens Industry Online Support entry and the S7-300 Module Data manual referenced at the end of this article.

Pinout and Terminal Layout

The 6ES7332-5HF00-0AB0 uses a single 40-pin front connector that is divided into two rows (terminals 1–20 on the upper row, 21–40 on the lower row). The module's terminal cover, when opened, shows the channel assignment as printed on the inside of the flap. The functional split is:

The 40-pin connector ships pre-numbered; do not re-stamp the terminals — the silkscreen inside the front door is the canonical reference. The two Mana terminals (19 and 39) are the analog-ground reference for each group and must remain connected to the field-side ground return of the actuator loop.

Power Supply Wiring Requirements

Each group on the SM 332 is electrically independent of the other. To energize the analog output drivers in group A you must land +24 V on terminals 1 (or 2) and 0 V on terminal 20. To energize group B you must land +24 V on terminals 21 (or 22) and 0 V on terminal 40. The 24 V source is typically:

• The same SITOP / PS 305 / PS 307 power supply that powers the CPU, sized for the total load of the rack plus all analog output groups
• Or a dedicated 24 V supply for the analog section if you want to ride through a CPU power fault with controlled analog outputs

Field practice: use one common 24 V return bus. The two 0 V pins (20 and 40) are not internally bridged on the module — they are isolated group returns. If you only use one supply, you must externally jumper pin 20 to pin 40 so that the group-B driver sees a defined return path. If you want the groups truly independent (e.g. one group is a safety-related reference and the other is non-safety), use two separate supplies and leave pin 20 and pin 40 isolated.

Wire gauge and torque

• Solid conductor: 0.25–2.5 mm² (AWG 24–14)
• Stranded with ferrule: 0.25–1.5 mm² (AWG 24–16)
• Tightening torque on the screw terminal: 0.4–0.7 N·m (3.5–6.2 lbf·in)
• Strip length: 8 mm

Channel Grouping and Per-Group Power

The fundamental rule — confirmed in the S7-300 Module Data manual — is that each group is energized by its own 24 V pair. The implications for installation are:

1. If you use only channels 0–3 (Group A): connect +24 V to pin 1, 0 V to pin 20. Pins 21/40 may be left open.
2. If you use only channels 4–7 (Group B): connect +24 V to pin 21, 0 V to pin 40. Pins 1/20 may be left open.
3. If you use all 8 channels: connect both pairs, or connect one supply and bridge 1↔21 and 20↔40 externally.
4. Pin 2 and pin 22 are parallel feed-throughs of pins 1 and 21. They are daisy-chain terminals used to pass 24 V to the next device in a row. Either one — pin 1 or pin 2 — is a valid +24 V landing point for group A; do not land two separate supplies on them.

The 24 V supply does not power the backplane logic. The S7-300 rack still receives its 5 V through the bus connector on the side of each module. The +24 V on the front connector is solely for the analog output driver stage, so a tripped external 24 V breaker will silence the analog outputs but leave the CPU running and the SF LED will appear on the affected group.

Step-by-Step Wiring Procedure

1. De-energize the rack and the analog 24 V supply. Lock and tag per local electrical safety rules.
2. Verify module order number on the side label is exactly 6ES7332-5HF00-0AB0. The label includes a 2D matrix code; scan it with the Siemens Industry Online Support app if available to confirm the variant.
3. Open the front door and lift the connector cover. The channel layout is printed on the inside of the cover; do not rely on terminal-block markings alone.
4. Pre-wire the 24 V supply pair for group A: 24 V → pin 1 (or 2), 0 V → pin 20. Use ferrules on stranded wire.
5. Pre-wire the 24 V supply pair for group B: 24 V → pin 21 (or 22), 0 V → pin 40. If group B is unused, leave both pairs open; do not stub them with jumpers to the field side.
6. Land each analog output: connect either QVn (voltage mode) or QIn (current mode) to the actuator's positive input, and Mn to the actuator's negative/return. Leave the unused pin (QV or QI) open; do not strap them together.
7. Where the actuator needs a 4-wire connection for long cable runs, wire S+n back to the actuator's remote-sense terminal. The S+ pin is high-impedance and carries no load current; its purpose is to compensate for voltage drop on long QV runs. Leave S+ open for short runs (<10 m) and for all current-mode outputs.
8. Torque every screw to 0.6 N·m. Tug-test each wire.
9. Close the front door so that the terminal silkscreen matches the channel assignment.
10. Power up the 24 V supply first, then the rack. Confirm the SF LED is off on both groups.

Output Type Configuration

The wiring is only half the story — each channel must also be configured in STEP 7 / TIA Portal for the type of output you wired. The driver stage on the 6ES7332-5HF00-0AB0 is shared between QV and QI; setting the wrong output type in software will produce a short-circuit fault or an out-of-range value at the actuator. Configuration is per channel via HW Config (STEP 7 V5.x) or the device view (TIA Portal):

Shielding and Grounding Best Practice

Analog signal integrity is highly sensitive to common-mode noise. Apply these rules:

• Use twisted-pair shielded cable (e.g. Belden 8761, 2-conductor) for each output run. Ground the shield at the cabinet end only — do not ground the actuator end of the shield (this avoids ground loops).
• Connect the cable shield to the S7-300 subplate using a shield clamp and pigtail shorter than 50 mm. The subplate itself must be bonded to the cabinet PE bus with a low-impedance strap.
• Run analog output cables in a separate conduit at least 200 mm from VFD output cables, motor wiring, and any cable carrying >10 A switching transients.
• Keep the analog 24 V supply ground return (pin 20 or 40) bonded to the same PE star point as the CPU 24 V return. Floating the analog return creates a common-mode voltage that pushes the analog signal out of the ±10 V / ±20 mA range.

Common Wiring Errors and Their Symptoms

Diagnostic LED Behavior

The 6ES7332-5HF00-0AB0 has three LEDs on the front:

• SF (red) — Group fault: missing 24 V on the relevant group, output short, configuration error, channel fault, or wire break (in current mode only, if diagnostics are enabled in the software).
• Group A LED (green) — On when group A is configured and the 24 V supply is present on pins 1/20.
• Group B LED (green) — On when group B is configured and the 24 V supply is present on pins 21/40.

The diagnostic interrupt can be enabled in HW Config. When enabled, an incoming SF condition writes a diagnostic entry to the diagnostic buffer of the CPU and a corresponding OB82 (diagnostic interrupt) is triggered. In the OB82 local variables you will see:

• OB82_MDL_ADDR — logical base address of the module (e.g. PQW 256)
• OB82_IO_FLAG — incoming (TRUE) or outgoing (FALSE) event
• Channel-specific fault bits in the diagnostic data record DS0/DS1 — accessible via SFC 59 / RD_REC

Verification and Commissioning

1. With the 24 V supply live and the CPU in STOP, use a DMM to measure 24 V across pins 1–20 and 21–40. Both should read between 20.4 V and 28.8 V (the S7-300 24 V tolerance per the S7-300 Module Data manual).
2. Watch the SF LED. It should remain off. A solid red SF means one or both groups lack 24 V or have a wiring fault.
3. From STEP 7 / TIA Portal, open the module's online diagnostics. Confirm that the slot is reporting "Module OK" and the channel status is "OK".
4. Place the CPU in RUN. Force each PQW to a known value (e.g. 0, mid-scale, full-scale) and verify the field voltage or current with a calibrated process meter.
5. For current loops, break the loop and insert the meter in series with QI and M. For voltage outputs, meter across QV and M.
6. Step the value slowly and verify linearity: at 0 % you should see the low end of the range; at 100 % you should see the high end; at 50 % you should see the midpoint. Non-linearity beyond ±0.3 % of full scale typically indicates a grounding or shield issue, not a module fault.

Comparison with Neighbouring SM 332 Variants

The 2- and 4-channel variants use a single 24 V pair (pins 1 and 20 on a 20-pin connector). The 8-channel variant introduces a second 24 V pair (pins 21/40) and is the only one that requires the daisy-chain supply decision. When migrating from a 4-channel 6ES7332-5HD01-0AB0 to the 8-channel 6ES7332-5HF00-0AB0, double the connector wiring schedule and recheck the 24 V supply sizing: a fully loaded 8-channel module drawing 20 mA per channel can pull up to 160 mA from each group's 24 V feed.

Field-Proven Caveats

• The 24 V return pin (20 or 40) and the Mana pin (19 or 39) are not the same node. Pin 19/39 is the analog ground reference of the DAC; pin 20/40 is the 24 V power supply return. They are typically bonded internally on the module, but if you isolate them externally (e.g. by using a separate isolated DC/DC converter for the 24 V), the analog ground must still return to the same star point or the output saturates.
• The maximum load on a voltage output is 5 mA. Exceeding this on a long cable run will pull the QV output below the commanded value. Switch to a current loop (QI) for runs longer than approximately 50 m or for actuators with input impedance below 2 kΩ.
• The maximum loop impedance on a current output is 600 Ω at 20 mA. The voltage compliance of the current driver is approximately 15 V, so for a 24 V supply the headroom is reduced — verify the actuator's burden spec.
• If the actuator requires a 0–10 V signal but you only have a 4–20 mA input, the cleanest fix is to wire a 500 Ω precision resistor across QI and M and convert the current to a voltage (0.5 V at 1 mA, 10 V at 20 mA). Do not try to share a single channel between a voltage and a current load.