Application Scenarios
In a 420 MW coal unit that still runs S5-155H for its burner management system (BMS), the original UR2-H rack — a 6ES5188-3UH51 dry chassis populated with two 155H CPUs in redundant pair, an IM 308C PROFIBUS head, and a mix of SM 150/160 I/O — had survived 22 years before a backplane anomaly surfaced. During a forced-outage valve-lobe test, the lead CPU’s I/O scan started throwing sporadic “bus parity” faults on the right-hand 11-slot segment. The instrumentation team suspected the backplane’s gold-finger edge connectors — the rack had lived through two major cabinet washes (HP wash + chemical clean) and the 5 V bus trace on Position 17 showed 30 mV higher drop than Position 3. Rather than re-terminating 168 I/O wires into a new pre-populated rack (which would have meant a 14-hour BMS recertification), the plant sourced a bare 6ES5188-3UH51 dry chassis, transferred the existing 6ES5955-7AA11 PSU, the fan tray, both 155H CPUs, and all I/O modules onto the fresh backplane in 3 hours during the outage window, and re-commissioned with a single cold-start. The split 10+11 topology meant the left segment (CPU A + IM + critical DI for flame scanners) and right segment (CPU B + SOE + DO to fuel trip solenoids) stayed logically identical — no rewiring, no reparameterization. For this BMS bay, the 6ES5188-3UH51 wasn’t a module — it was the difference between a 3-hour swap and a 3-day recert.
Parameter
| Main Parameters | Value/Description |
|---|---|
| Product Model | 6ES5188-3UH51 |
| Manufacturer | Siemens (SIMATIC S5 Series) |
| Product Category | Central Rack / Universal Rack (UR2-H) |
| System | SIMATIC S5-155H (High-Availability) |
| Slot Configuration | 10 + 11 split segments (21 positions total) |
| Included Items | Chassis + backplane ONLY (no PSU, no fan, no CPU, no battery, no manual) |
| Backplane Bus | S5 system bus (address/data/control), DIN 41612 connectors |
| Compatible PSU | 6ES5955 series (24 V DC input, 5 V / 2×14 A for 155H) |
| Compatible Fan | S5-155H dedicated fan module (mounts in fan slot) |
| Mounting | 19″ rack-mount or DIN-rail via adapter; cabinet IP20 |
| Dimensions (approx.) | 480 × 330 × 230 mm (19″ × 13″ × 9″) |
| Weight (approx.) | ~7.3 kg (empty chassis) |
| Operating Temp. | 0 °C to +60 °C (forced-air required via fan module) |
| Cooling | Forced convection (fan module mandatory in populated configs) |
Note: “3UH51” = UR2-H, S5-155H, without PSU & without fan. The “H” denotes High-Availability (redundant CPU architecture). For the same chassis pre-loaded with PSU + fan, see 6ES5188-3UH31. The 6ES5188-3UH51 is the “bare metal” option when you want to reuse existing PSU/fan or when the PSU rating (24 V DC vs. 120/230 V AC, 18 A vs. 40 A) needs to be specified independently.
Technical Principles and Innovative Values
- Innovation Point 1 – Split 10+11 Backplane for HA CPU Pairing. The 6ES5188-3UH51 isn’t a generic 21-slot frame — the backplane is electrically partitioned into a 10-slot left segment and an 11-slot right segment, each hosting one of the two 155H CPUs in a redundant “H” pair. The backplane handles the reflection bus (Spiegelbus) that synchronizes the two CPUs’ I/O images — if CPU A faults, CPU B takes over with <1 scan loss. This split topology is why the 155H could achieve SIL 2–3 class availability in burner management and turbine protection when standard S5-155U could not.
- Innovation Point 2 – “Dry Chassis” Decouples PSU/Fan from Mechanical Life. By shipping the 6ES5188-3UH51 without PSU and fan, Siemens let plants spec the power and cooling independently: a 155H in a temperate control room might run a 5 V / 18 A PSU; the same 155H in a tropical MCC room with heavy I/O load might need 5 V / 40 A. The fan module, too, wears mechanically (bearings) on a different curve from the backplane (gold-finger oxidation). Separating them means the 6ES5188-3UH51 chassis can outlive two generations of PSUs — a design philosophy that pays off in 25-year-old plants still running S5.
- Innovation Point 3 – DIN 41612 Auto-Pierce Backplane Connectors. All S5 modules (CPU, IM, SM, FM, CP) seat via DIN 41612 H15-style connectors with automatic insulation-displacement (IDA) or press-fit gold pins on the backplane. The 6ES5188-3UH51 backplane is a multi-layer PCB with gold-flashed contacts — the 5 V distribution traces are beefy enough for 2×14 A (dual PSU reflect), and the address/data/control lines are terminated per S5 bus timing. In practice, this means a module pulled from a 6ES5188-3UH51 seats into any S5-155H/155U/135U UR2 without reparameterization — the “universal” in UR2-H.
- Innovation Point 4 – 19″ Standard + DIN Hybrid Mounting. The 6ES5188-3UH51 chassis accepts both 19″ rack ears and DIN-rail adapters, making it at home in a European-style Schaltschrank (TS 8 frame) or a North-American freestanding MCC line-up. For retrofit projects migrating an S5-155H bay into a newer T3000 cabinet, this mounting flexibility avoids having to re-drill the enclosure — just transfer the 6ES5188-3UH51 onto the new bay’s DIN strip.
