Avoiding pitfalls in procurement for controlled environment temperature and humidity monitoring: 5 types of parameters are not clearly written, leading to rework during the acceptance phase

[Core Summary]

The rework related to controlled environment temperature and humidity monitoring often stems from vague technical agreements. There are five points of contention: the accuracy indicators lack reference conditions, the calibration cycle is not specified, the installation location lacks representative justification, the output protocol does not match the system, and there is a conflict between the protection level and cleaning method. This article uses the sample parameters of the S+S Regeltechnik RFTM and AFTF series as benchmarks to provide a checklist and sample clause writing.

[Text]

Pitfall 1: Accuracy metrics are divorced from reference conditions

The technical agreement often only states "humidity accuracy ± 2%", which leads to discrepancies during acceptance inspection. The sample writing includes conditions: AFF/AFTF standard type ± 2.0% (20...80% RH, +25°C), ± 3.0% outside the range; -20/-25 type ± 1.8% (10...90% RH), ± 2.0% outside the range. For temperature, the standard type is ± 0.4 K, and the -20/-25 type is ± 0.2 K, both referenced to +25°C.

Writing of terms: The accuracy value must be accompanied by the humidity range and reference temperature, with indicators outside the range listed separately.

Pitfall 2: Blankness in calibration responsibility and cycle

The sample indicates that the calibration has been completed at the factory and can be fine-tuned on-site by professionals; the long-term stability is ± 1% per year. The AFTF-Modbus-T3 zero offset adjustment is ± 10% relative humidity (RH) and ± 5°C.

Terms and conditions: Clarify the method for providing factory calibration certificates, the party responsible for on-site calibration, the recalibration cycle (based on ±1% drift per year and internal control limits), and the archiving of calibration records.

Pitfall 3: Lack of representative argumentation for installation location

The room-type and duct-type models are not interchangeable. The RFTM/RFTF room-type models feature an ABS shell, IP 30 rating, and are designed for surface mounting on walls or concealed installation in a Ø55 mm box. The AFTF series models are made of glass fiber-reinforced polyamide, with an IP 65 rating, and come equipped with a Ø16 mm V2A protective tube, suitable for use in ducts and outdoors.

Writing of terms: List the installation elevation, distance from the air supply outlet, and airflow path avoiding door openings for each room, and specify the basis for point density.

Pitfall 4: Output protocol does not match existing systems

The boundaries between analog and digital quantities differ. For Type I 4...20 mA, the operating resistance Ra needs to be calculated as (Ub – 14 V) / 0.02 A; for Type U 0–10 V, the load requirement is > 5 kΩ. Modbus is an electrically isolated RS485, RTU protocol, with slave addresses ranging from 0 to 247. The baud rate and address are set via DIP switches during power-off, and LA terminators are equipped at the ends.

Article writing: Specify the protocol type, baud rate, parity bit, address allocation table, and terminal resistance configuration. For analog quantity points, indicate the range gear (AFTF temperature has four gears, DIP, with a default of 0...+50 °C).

Pitfall 5: Conflict between protection level and cleaning method

The IP 30 enclosure is not spray-proof. The room-type IP 30 can be used for wall wiping and disinfection; if there is flushing or atomization disinfection, it is necessary to change to an IP 65 structure or add a protective cover.

Article writing: Incorporate the cleaning and disinfection process into the technical agreement annex, and the supplier shall confirm the compatibility of the protection level based on this.

Synchronized verification of supporting differential pressure measurement points

The pressure difference gradient in clean rooms is often implemented concurrently with temperature and humidity control. PREMASGARD 111x / 112x utilizes piezoresistive elements with temperature compensation and offers an eight-range DIP switchable measurement scale; the typical output for models 1111 / 1121 (1000 Pa range) is ± 10 Pa, while for models 1115 / 1125 (5000 Pa range), it is ± 50 Pa. The output ranges from 0–10 V or 4…20 mA.

[Parameter Table]

Check items

S+S Regeltechnik Sample Parameters

Pitfalls to be avoided

Humidity range

Both RFTM and AFTF range from 0 to 100% relative humidity

If only the measuring range is considered without considering the allowable operating humidity, and the device is installed in an area close to saturation, condensation may occur

Allowable operating humidity

RFTM-PS-Modbus 0...95% RH; AFTF < 95% RH (both without condensation)

If the purified water room and cleaning room exceed this limit, they should still be selected based on the room type

Humidity Accuracy Level

± 2.0 % (20...80 % RH, +25 °C), ± 3.0 % outside the range; -20 / -25 models ± 1.8 % (10...90 % RH)

The agreement only specifies ± 2%, omitting the range and reference temperature, leading to disputes during acceptance inspection

Temperature range

AFTF 4-position DIP: –35…+35 / –35…+75 / 0…+50 / 0…+80 °C, default 0…+50 °C; RFTM 0…+50 °C

The on-site DIP setting is inconsistent with the DCS configuration scale, resulting in systematic deviations

Temperature accuracy

RFTM ± 0.2 K; AFTF Standard ± 0.4 K; -20 / -25 Models ± 0.2 K (all at +25 °C)

Quoted as per the standard model, but accepted within ± 0.2 K

Calibration and Long-term Stability

Factory calibrated; long-term stability ± 1% per year; AFTF-Modbus-T3 zero offset ± 10% RH / ± 5°C

The recalibration cycle and traceability chain have not been agreed upon, making it impossible to provide evidence during the audit

Installation location

Room-type wall surface surface-mounted or Ø55 mm concealed box; pipeline-type protective tube Ø16 mm V2A, NL 55 / 88.5 / 137 mm

When installed directly beneath the air supply outlet or on the airflow path of the door opening, the readings are not representative

Point density

For room-type samples, it is recommended to have one unit per 30 m²

Following the early layout and using the old locations, blind spots in monitoring emerged after the room renovation

Output Protocol (Simulation)

0–10 V（RL > 5 kΩ）；4…20 mA（Ra = (Ub – 14 V) / 0.02 A）

The operational resistance of the long line has not been calculated, resulting in an undervoltage in the current loop

Output Protocol (Digital)

Modbus RTU, RS485 electrical isolation, address 0...247, DIP power-off setting

Hot address change causes bus conflict; LA terminator not configured

Power Supply

RFTM 24 V AC / DC（± 10 %）；AFTF 24 V AC（± 20 %）/ 15…36 V DC

The power capacity is directly calculated by multiplying the number of units, without allowing for surge and redundancy margins

Power consumption

RFTM typical < 4.4 W / 24 V DC; AFTF < 1.1 VA / 24 V DC

Estimate the power supply for mixed-configuration models based on the same power consumption

Protection level

RFTM / RFTF IP 30；AFTF IP 65；PREMASGARD 111x / 112x IP 67，112x-SD IP 54

The disinfection method conflicts with the protection level, resulting in liquid ingress into the enclosure

Protection category

III（EN 60730）

No comparison with on-site safety level requirements has been made

Differential pressure measurement point accuracy

1111 / 1121 (1000 Pa range) typical ± 10 Pa; 1115 / 1125 (5000 Pa range) typical ± 50 Pa

Measure a pressure difference gradient of 10 Pa level using a 5000 Pa range gear

Warm-up / Response Time

RFTM preheats for approximately 1 hour, with a response time of less than 2 minutes

The alarm delay is shorter than the response time, and the door opening disturbance triggers a false alarm

Safety-related applications

The sample indicates that the RFTM series should not be used as safety-related equipment

Directly connected to the safety interlock circuit

Collection Cycle and Alarm Threshold

[Please verify]

Not solidified in the agreement, subject to repeated adjustments after delivery

**Parameter Source Description**: The values for range, accuracy, power supply, protection level, insertion length, and pressure differential range in the table are all actual PDF values, taken from official samples of S+S Regeltechnik: AFTF, AFTF-Modbus-T3, RFTM-PS-Modbus, RFTF, and PREMASGARD 111x / 112x / 112x-SD (all versions Rev. 2022–2025 GB). The acquisition cycle and alarm thresholds are configured on the project side and are not covered in the samples; marked with [Please verify].