[Core Summary]
The solid dosage clean zone originally employed manual inspection and meter reading, resulting in data discontinuities between shifts and a lack of continuous curve support during deviation investigations. The S+S Regeltechnik (S+S, Germany) RFTM series Modbus temperature and humidity transmitters, connected to the monitoring platform via an RS485 bus network, feature a humidity range of 0 to 100% RH with a typical deviation of ±2.0% (20...80% RH, +25°C) and a temperature range of 0...+50°C with a typical deviation of ±0.2 K. After the transformation, temperature and humidity data shifted from manual sampling to continuous collection, with recording periods and alarm thresholds uniformly configured on the platform side. (This article serves as a typical application reference, with equipment parameters sourced from official samples. The number of points and compliance rates are project implementation data and subject to verification, and are not specific project delivery commitments.)
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Background and Pain Points
The clean zone of the solid dosage workshop manually records temperature and humidity by shift, which presents three specific issues. Firstly, the sampling interval is measured in hours, and short-term fluctuations in the dehumidification section of the air conditioning unit cannot be captured, leading to a lack of process data for deviation investigation. Secondly, there is a need for secondary entry between paper records and electronic batch records, and data consistency relies on manual verification. Thirdly, the original distribution of measurement points was determined based on the early layout, and no synchronous adjustment was made after room renovation, resulting in a lack of representative measurement points in some areas.
Solution and Deployment
Selection of Measurement Points
The RFTM series Modbus version is selected for measurement points within the clean room. This model features an ABS casing, dimensions of 98 × 98 × 33 mm, and a protection level of IP 30. It supports surface mounting or installation in a Ø55 mm concealed box, meeting the requirement for easy wiping of clean room surfaces. For humidity and temperature measurement, a digital humidity sensor integrated with a temperature sensor is used. It exhibits low hysteresis and good long-term stability, and has been pre-calibrated at the factory. The point density is based on the recommended values provided in the sample, with one device configured per 30 m² of room area.
The return air section of the air conditioning unit connected to the clean room is selected from the AFTF series. The casing is made of 30% glass fiber reinforced polyamide, with a protection level of IP 65. It is equipped with a Ø16 mm V2A stainless steel protective tube and a replaceable sintered filter, suitable for the wind speed and dust conditions within the duct.
Bus and Power Supply
The RFTM series Modbus version employs an electrically isolated RS485 interface, Modbus RTU protocol, with a slave address range of 0…247. The baud rate and address are set via DIP switches during power-off, avoiding bus conflicts caused by live address changes. A LA bus terminator (order number 1906-1300-0000-100) is added at the end of the bus as an active terminal. The power supply is 24 V AC / DC (± 10%), with a typical power consumption of < 4.4 W per 24 V DC unit. The power capacity and redundancy mode are determined based on branch statistics. Wiring uses 0.2–1.5 mm² push-in terminals.
Alarms and Logging
On the platform side, temperature and humidity upper and lower limits, as well as deviation alarm delays, are set according to room levels. On the device side, the preheating time is approximately 1 hour, and the response time is < 2 minutes. The alarm delay setting needs to be greater than the response time to avoid triggering invalid alarms due to instantaneous disturbances when opening doors. The zero offset and annual recalibration cycle are determined based on the long-term stability indicator of ± 1% per year.
Results and Value (Illustrative)
After the renovation, the temperature and humidity monitoring in the clean zone has shifted from shift-based sampling to continuous data collection. Historical curves can be directly exported for deviation investigations and annual reviews. Manual meter reading and secondary data entry have been eliminated, ensuring record consistency through the system. The density of measurement points has been reevaluated based on area, encompassing the newly added isolation zones post-renovation. The specific number of points and the extent of compliance improvement are subject to the on-site acceptance report.
One point to note: The sample clearly indicates that the RFTM series should not be used as safety-related equipment, and independent instruments should be separately configured for interlocking and safety protection circuits.
[Parameter Table]
**Parameter Source Description**: The device parameters are taken from the official sample RFTM-PS-Modbus (Rev. 2022-V31 GB) and AFTF (Rev. 2025-V29 GB) provided by S+S Regeltechnik. The number of points, compliance rate, acquisition cycle, and alarm delay are project implementation data, marked [please verify], and are subject to the on-site acceptance report.
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