SIEMENS 7MH4950-2AA01
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SIEMENS | PLC Controls | Function Modules
- EICHLER-art.no.: K0204909
- EAN: 4019169840040
Product description
SIWAREX U WEIGHING ELECTRONICS (TWO-CHANNEL VERSION) * FOR CONNNECTING TWO SCALES * FOR SIMATIC S7-300 AND ET200M * RS232 INTERFACE FOR CONNECT. OF A PC * TTY INTERFACE FOR REMOTE DISPLAY CONNECTION WITH BUS CONNECTOR
Services for SIEMENS 7MH4950-2AA01
Repair
from 590,23 €
to 1.062,41 €
Replacement
1.585,80 €
Used
1.762,00 €
New
1.938,20 €
SIEMENS |
7MH4950-2AA01 –
additional product information
| Delivery information | |||
|---|---|---|---|
| Export identifier | AL: N ECCN: EAR99I | ||
| Net weight | 0.24 | ||
| Quantity | 1 Stück | ||
| Packaging quantity | 1 | ||
| Additional product information | |||
|---|---|---|---|
| Product status | EOP: 2025-10-01 | ||
| EAN | 4019169840040 | ||
| UPC | / | ||
| Static lot number | 85389091 | ||
| List indicator | WT10 | ||
| Product group | 4849 | ||
| Country of origin | DE | ||
| Compliance with the substance restrictions according to RoHS directive | Since: 20071107 | ||
| Product classifications | Version | Classification | |
|---|---|---|---|
| eClass | 4 | 27-27-21-XX | |
| eClass | 5.1 | 27-32-03-90 | |
| eClass | 6.0 | 27-32-03-01 | |
| ETIM | 3 | / | |
| ETIM | 4 | / | |
| ETIM | 5 | / | |
What is the 7MH4950-2AA01 and where is it used?
The 7MH4950-2AA01 is the dual-channel SIWAREX U weighing assembly from Siemens for SIMATIC S7-300 and ET 200M systems. It is used in applications where two separate platform scales, vessel scales or bunker scales, or two analogue force-measurement points with strain-gauge load cells need to be processed. Typical applications include level monitoring of silos and bunkers, load and force measurement, and static weighing tasks in production and conveying processes. For maintenance engineers, an important advantage is that weight values can be processed directly within the PLC, while diagnostic functions are fully integrated into the automation system. For purchasing and production departments, the article number is clearly assigned to a dual-channel SIWAREX U version. It should be noted that the assembly is not approved for legal-for-trade applications in accordance with OIML R76.
Overview of the key technical data and what it means
Technically, the 7MH4950-2AA01 is designed for 24 V DC operation and, in the dual-channel version, requires a maximum current of 240 mA. The assembly processes analogue load cells with an output range of 1 to 4 mV/V, supplies them with 6 V DC excitation voltage and supports a permissible load-cell resistance per channel of greater than 40 Ω and less than 4,010 Ω. An update rate of 50 Hz, corresponding to a measurement time of 20 ms, ensures fast response times, while an error limit of ≤ 0.05% and an internal resolution of 65,535 divisions provide stable and highly accurate measurement values. Other important practical features include a maximum load-cell cable length of 500 m, integrated RS232 parameterisation and an IP20 enclosure rating for control-cabinet installation.
Product status, life-cycle status and obsolescence
For operators of existing systems, the product life cycle is a particularly important consideration. Siemens still references SIWAREX U in catalogue documentation; however, the SIOS portal lists the life-cycle status of the 7MH4950-2AA01 as “Product Cancellation” and refers to a product notice concerning the discontinuation of S7-300 and ET 200M components. From a spare-parts strategy perspective, this means that the assembly remains relevant for existing systems but should be actively incorporated into Obsolescence Management and stockholding strategies. Siemens has also verified full software compatibility with older 7MH4601-1*A01 modules. Hardware compatibility is likewise maintained, although the newer generation operates with a 6 V load-cell excitation voltage instead of 10 V. Therefore, during migration projects, both the parameter settings and the connected load cells should be checked carefully.
Available EICHLER services and when they are relevant
For operators facing the risk of a breakdown, four options are particularly relevant for the 7MH4950-2AA01: repair, replacement, used parts and new parts. Repair is especially suitable when the existing assembly is already known within the system and can be economically retained. EICHLER states that its repair service includes technical cleaning, preventive maintenance, comprehensive functional testing and a minimum 24-month warranty. Replacement is the preferred option when production pressure is high and the machine must be returned to operation as quickly as possible. Used parts can be a cost-effective solution for spare-parts stockholding, while new parts are well suited to planned spare-parts strategies where maximum certainty regarding condition and service life is required. Particularly for discontinued or near-obsolete platforms, these services help maintain functionality, availability and supply security despite increasing obsolescence risks.
| Fault Description | Possible Solution |
|---|---|
| Why is the red SF LED on the 7MH4950-2AA01 permanently illuminated? | The red SF LED indicates an operating fault. First, check whether the external 24 V supply is present, whether the load-cell signal is within the permissible range and whether fault bits indicate conditions such as sense-voltage undervoltage, ADC faults or a missing 24 V supply. If the power supply is stable and the fault remains after checking the wiring and load cells, a defect within the assembly itself should also be considered. |
| Why does the SIWAREX U report “Minimum voltage at the sense line not reached”? | This message typically indicates a voltage drop between the assembly and the junction box, a cable break, missing wire links in a four-wire configuration or a short circuit within the wiring. Check the sense, signal and excitation lines for each channel systematically, inspect the junction box and ensure that the required links are correctly installed when using four-wire load cells. Only after the wiring has been verified and the load cell appears electrically sound should the assembly itself be suspected. |
| Why can’t I establish communication with the 7MH4950-2AA01 using SIWATOOL U? | The assembly uses an RS232 interface for parameterisation. At the terminal block, RXD1, GND1 and TXD1 are used, and Siemens specifies the 7MH4607-8CA connection cable for this purpose. During operation, the COM LED should flash when RS232 communication is active. If it remains off, the most common causes are incorrect cable wiring, serial-port configuration issues, USB-to-serial adapter problems or the use of the wrong interface. Therefore, verify the physical wiring first and then check the PC-side communication interface before assuming a communication fault within the assembly. |
| Why is the weight value unstable or fluctuating significantly? | When measurement values are unstable, the cable routing and EMC installation should be checked first. Siemens recommends separate routing of power and measurement cables, large-area shield connections at both ends, twisted wire pairs for the sense, signal and excitation lines, and a common reference potential throughout the system. In addition, the configurable low-pass and averaging filters can help reduce random interference. If multiple load cells are connected to a single channel, a junction box is also required to ensure correct electrical interconnection. |
| Why do I receive the message “Calibration command could not be executed”? | In many cases, the calibration points are too close together, an existing fault condition is present or the selected channel does not exist or is not active. Siemens specifies that the calibration weight must generate at least a 5% change in the load-cell output signal. Therefore, first verify that the correct channel is active, check whether the scale has already been calibrated and ensure that the selected calibration weight is sufficiently large. Any existing operating faults must be completely resolved before calibration can be performed successfully. |
Is the 7MH4950-2AA01 suitable for legally regulated weighing applications?
No. According to Siemens, SIWAREX U is not approved for legal-for-trade weighing in accordance with OIML R76. The assembly is intended for industrial static weighing and force-measurement applications where process integration, diagnostics and flexible parameterisation are the primary requirements. For applications subject to legal metrology regulations, the selection should therefore not be based solely on the article number or mechanical compatibility, but on the required certification of the complete weighing system.
Which load cells can be connected to the 7MH4950-2AA01?
Suitable load cells are analogue strain-gauge (SG) load cells with a sensitivity of 1 to 4 mV/V, provided that a 6 V excitation voltage is permitted. Siemens specifies a permissible load-cell resistance per channel of greater than 40 Ω and less than 4,010 Ω without an Ex interface. If multiple load cells are connected in parallel to a single channel, a junction box is required. For purchasing and maintenance teams, this is important because it allows compatibility, modification requirements and accessory needs to be assessed at an early stage.
Can I replace an older SIWAREX U 7MH4601-1BA01 with a 7MH4950-2AA01?
In principle, yes. Siemens describes the 7MH4950-AA01 generation as being fully software-compatible with older 7MH4601-1A01 modules, while hardware compatibility is also maintained. However, an important technical difference is the load-cell excitation voltage: the newer generation operates with 6 V instead of 10 V. Before carrying out a replacement, the load cells, parameter settings and existing calibration data should therefore be checked to ensure that the exchange can be completed without unexpected issues in the existing system.
Can the assembly be commissioned without calibration weights?
Yes. Siemens describes the use of theoretical calibration with SIWATOOL U, provided that the mechanical installation is functioning correctly and the measurement certificates for the individual load cells are available. Alternatively, known calibration data can be transferred via a data set, allowing identical scales to be returned to operation quickly. This is particularly useful for operators when on-site calibration with test weights would be logistically difficult or when an assembly replacement must be completed under significant time pressure.
Has the 7MH4950-2AA01 been discontinued, and how can supply continuity be ensured?
Siemens lists the 7MH4950-2AA01 in the SIOS portal with the life-cycle status “Product Cancellation” and links the assembly to the discontinuation notice for S7-300 and ET 200M components. This does not automatically mean that supply is no longer available, but it does indicate an increased procurement risk. A sensible strategy therefore combines inventory assessment, strategic stockholding and the planning of repair or replacement options to ensure that unplanned breakdowns remain manageable even in systems approaching obsolescence.
Can the 7MH4950-2AA01 be used in hazardous areas?
Yes, but with certain limitations. According to Siemens, the SIWAREX U can be installed directly in Zone 2 hazardous areas. For applications where the load cells are located in Zone 1, the SIWAREX IS Ex interface is required to provide intrinsically safe power to the load cells. For project planning, this means that not only the assembly itself but also the load cells, cabling and all associated approvals must be assessed as part of the complete system.
