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Sample Representation of Inline Process Transmitter
The inline process transmitter consists of a process transmitter and a sensor tube with an additional monitoring element for measuring the pressure between the support tube and the sensor tube.

The Principle of Sensor Monitoring

Normal Operation

In normal operation, pressure measurement and sensor monitoring function without restrictions within the performance limits of the overall system.

The space in the double tube system is evacuated. This vacuum is measured with the monitoring element. If the vacuum is intact, no alarm signal is emitted.

Sensor Monitoring

In the event of a sensor break, the monitored pressure in the space between the double tube system rises. This change is continuously measured, registered, and displayed by the process transmitter.

The alarm signals on the current loop are also output via the HART® protocol, depending on the version. This WIKA double tube system is the solution for critical process flows where neither the measuring medium should enter the environment nor the product should be contaminated.

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Alarm signal of sensor monitoring Pressure increase in the interspace of the double-pipe system
≥ 100 … < 300 mbar
[≥ 1.45 … < 4.35 psi]
≥ 300 mbar
[≥ 4.35 psi]
Display and control unit Alarm message: “Membrane break” Alarm message: “Membrane break”
Current output, 4 … 20 mA No signal adjustment Fault current
Depending on the setting 3.5 mA or 21.5 mA
HART® communication Device status: “Membrane break” Device status: “Membrane break”


Technical Data


Inline Process Transmitter
Process wetted Sensor tube and process connection CrNi steel 1.4435 (316L)
Not process wetted Support tube: CrNi steel
Other materials, see housing head, electrical connection, and display and control unit, type DI-PT-U
Surface Quality
Process wetted Sensor tube and process connection
  • Ra ≤ 0.76 µm [30 µin] according to ASME BPE SF3
  • Ra ≤ 0.38 µm [15 µin] according to ASME BPE SF4, electropolished
Process wetted weld seams meet the requirements of ASME BPE 2022 chapter 6 part MJ
Housing Head
Plastic housing (PBT) with conductive surface according to EN 60079-0:2012, color: midnight blue RAL5022
CrNi steel housing 1.4308 (CF-8), precision casting
CrNi steel housing 1.4308 (CF-8) with electropolished surface (suitable for pharmaceutical, food, and hygiene sectors)

Measuring Range

Nominal measuring range 0 … 16 bar [0 … 200 psi]. Other measuring ranges are achieved via turndown. The smallest span for turndown is 4 bar [58 psi] and can be freely selected within the nominal measuring range.

For example, the device can also be set to 0 … 6 bar [0 … 100 psi] or -1 … +6 bar [-14.5 … +100 psi].

Relative Pressure
bar 0 … 16
psi 0 … 200
Vacuum and +/- Measuring Ranges1)
bar -1 … +15
psi -14.5 … +200
1) Under vacuum, sensor monitoring is only possible to a limited extent
Absolute Pressure
bar 0 … 16
psi 0 … 200

Vacuum/Overload Safety
Vacuum resistance Yes
Overload safety1) ◾ 1.5 times for process fluid temperature ≤ 70 °C [≤ 158 °F]

◾ 1.2 times for process fluid temperature > 70 °C … ≤ 150 °C [> 158 °F … ≤ 302 °F]
Maximum allowable pressure (PS) Corresponds to the end value of the measuring range (max. 16 bar [232 psi])
1) Related to the nominal measuring range

Output Signal
Signal Types 4 … 20 mA with HART®-Signal (HART®-Rev. 7)
4 … 20 mA
Load in Ω ≤ (U+ – 12 V) / 0.023 A (Non-Ex version)
U+ = Applied supply voltage (~ See “Auxiliary Power”)
Damping 0 … 99.9 s, adjustable
After the set damping time, the device outputs 63% of the pending pressure as an output signal.
Settling Time t99 Without HART®: 60 ms
With HART®: 80 ms
Update Rate Without HART®: 20 ms
With HART®: 50 ms

Process Connection
Standard Clamp connection according to DIN 32676
Clamp connection according to ASME BPE
Aseptic pipe screw connection according to DIN 11864-1, with threaded nozzle
Aseptic clamp connection according to DIN 11864-3, with flange clamp nozzle
Aseptic clamp connection according to DIN 11864-3, with groove clamp nozzle
Further process connections on request

Accuracy Information Accuracy under reference conditions1): 1 % of span
Zero Point -20 … +95 % (downwards adjustability is always limited by the minimum pressure of 0 bar abs. [0 psia])
Span -120 … +120 % with a difference between zero point and span of max. 120 % of the nominal measuring range including overload
Turndown Maximum recommended turndown 4:1
Non-Repeatability ≤ 0.3 % of span at nominal measuring range or recommended turndown
Behavior at Turndown
TD ≤ 4:1 No influence on accuracy
Long-Term Stability ≤ 1 % of span
1) Including non-linearity, hysteresis, zero point and end point deviation (corresponds to measurement error according to IEC 62828-2).

Sensor Monitoring via DTM

  • A DTM is available for the HART® output signal according to the FDT standard.
  • The DTM provides a self-explanatory and clear user interface for all adjustment and monitoring processes of the transmitters.
  • Process values can also be simulated for testing purposes and the parameter data can be archived.
  • A measurement recording is available for diagnostic purposes.

Example Diagnosis: Sensor Tube Break

In the event of a leaking sensor tube, the pressure monitored in the interspace of the double tube system increases.

If this monitoring pressure exceeds certain values, a warning signal is first transmitted, and if the pressure continues to rise, an alarm signal is sent.

This enables the user to perform a precise second-by-second error analysis.

The user thus has the advantage of minimizing potential production errors.

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