Self-Calibrating Temperature Sensor Prevents Undetected Drift

The Endress+Hauser iTHERM TrustSens hygienic RTD self-calibrates to verify in-line that the sensor is working as designed.
Dec 12, 2017
By Pharmaceutical Technology Editors

Endress+Hauser’s iTHERM TrustSens hygienic resistance temperature detector (RTD) is a self-calibrating temperature sensor that can be used in bio/pharma processes to eliminate the risk of undetected measurement drift. TrustSens’ self-calibration process functions in situ and provides the necessary documentation to meet regulatory requirements.

Traditionally, calibration cycles for standard temperature sensors in critical hygienic service are every six to twelve months, which leaves the potential for undetected drift in the sensor between cycles.  Such undetected drift could lead to product quality issues or even a complete loss of the production run.  Many hygienic and aseptic processes require equipment cleaning on a regular basis with sterilize-in-place (SIP) procedures, typically after every batch. The new temperature sensor is calibrated after every SIP cycle, which eliminates the risk of an undetected calibration drift and the risk of bad batches. It also reduces the need for frequent calibrations by verifying the sensor is working as designed in between manual calibration cycles.

TrustSens has a built-in, high-precision ceramic reference based on the Curie Point of the reference material, which is the temperature at which its ferromagnetic properties abruptly change. The change can be detected electronically. For applications using SIP operations—where steam at 121 °C (250 °F) is used to sterilize equipment—the sensor uses a reference material with a Curie Point of 118 °C (244 °F).  When the SIP process reaches 118 °C, the reference sensor in TrustSens sends a signal. Simultaneously, the TrustSens RTD measures the temperature.  Comparison between these two values is a calibration, identifying errors in the temperature sensor. If both sensors see 118 °C, the RTD sensor is still in calibration.  If the measured deviation is outside set limits, the device issues an alarm or error message and displays a light on the device.

Up to 350 calibrations can be stored, which can be submitted to regulatory agencies for verification of compliance issues. The device can also produce printable and uploadable audit-proof calibration certificates using asset management software such as Endress+Hauser’s FieldCare.

The sensor has built-in Heartbeat Technology to monitor the sensor and send warnings when it detects a sensor failure, drift, or other measurement errors. The TrustSens sensor measures temperatures from -40 to 160 °C (-40 to 320 °F), works in pressures up to 725 psi, and provides a 4-20 mA output with HART. The 4-20 mA output represents the measured process variable, and the HART signal contains diagnostic and status information.

The sensor is available with a variety of hygienic process connections.  It can also be configured for direct immersion measurement or with a protective thermowell for easy removal from the process.

Source: Endress+Hauser

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