A level value may be required at several points within a process plant. The plant operator wants to see the liquid level directly at the vessel. At the same time, the PLC requires a continuous measured value for visualization, control or trend recording. In addition, a MIN and a MAX limit level should trigger an alarm or switching function independently of the analog measured value.
A magnetic bypass level indicator can combine these functions within one common mechanical measuring point.
The basis is a bypass chamber mounted on the side of the vessel. It is connected to the vessel via at least two process connections and operates according to the principle of communicating vessels. Under suitable process conditions, the liquid level in the bypass chamber therefore follows the level in the vessel.
Inside the bypass is a float with a permanent magnet system. Its magnetic field acts through the wall of the bypass chamber. This allows the level to be transmitted to the outside without a direct electrical or mechanical penetration.
This single float movement can be used for several functions. An externally mounted magnetic display visualizes the level directly on site and requires no electrical power supply. An additionally mounted level transmitter converts the float position into a continuous electrical signal. Magnetic switches can simultaneously monitor defined limit levels.
At first glance, this creates three redundant sources of information about the same process value. However, an important distinction must be made here.
Local indication, continuous remote signal and limit switches have partially separate display, electronics and signal paths. They can therefore be used very effectively for mutual plausibility checking. However, all three functions are generally dependent on the same float and the same bypass chamber.
If the float becomes blocked or the bypass chamber is hydraulically isolated from the vessel, several signal paths can simultaneously indicate the same incorrect level.
The key point is: A magnetic bypass indicator with transmitter and switches provides very valuable functional redundancy between local indication, continuous remote measurement and limit-level signaling. However, for truly independent measurement redundancy, the common dependence on the bypass chamber and float must also be taken into account.
Table of Contents
- How does a magnetic bypass level indicator work?
- What is the function of the local magnetic display?
- How is the float position converted into a remote signal?
- How do additional magnetic switches work?
- Direct comparison of local indication, transmitter and limit switches
- What does redundancy actually mean with a bypass indicator?
- Why the common float remains a common source of failure
- When does the bypass level actually correspond to the vessel level?
- Why is the density of the medium decisive for the float?
- How temperature, viscosity and insulation influence the bypass
- Correctly define the measuring range and process connections
- Correctly scale the 4–20 mA signal
- Selecting a reed or magnetostrictive transmitter
- Using MIN and MAX switches effectively
- Using three signal paths for plausibility checking
- When a second independent measuring principle is required
- Systematically commissioning the measuring point
- Systematically diagnosing typical fault patterns
- Suitable WIKA / KSR Kuebler level measurement technology from ICS Schneider
- Conclusion
- Frequently asked questions about bypass indicators with transmitters and switches
1. How does a magnetic bypass level indicator work?
A magnetic bypass level indicator essentially consists of a vertical bypass chamber, at least two process connections and a movable float inside it.
The lower process connection connects the liquid space of the vessel with the bypass chamber. Depending on the design, the upper connection provides the connection to the upper section of the vessel or the necessary pressure equalization.
As a result, essentially the same hydrostatic liquid level is established in the bypass as in the vessel.
The float follows this level. Inside it is a permanent magnet system that transmits its magnetic field through the non-magnetic wall of the bypass chamber to the outside.
The major advantage of this design is that different display and sensor components can be mounted externally on the pressure-bearing bypass chamber. The chamber does not need to be mechanically penetrated for each individual measuring function.
With the WIKA model BNA, for example, the magnetic field of the float operates the externally mounted magnetic display. At the same time, continuous level transmitters and magnetic switches can also be mounted externally on the bypass.
The float therefore forms the central mechanical information element of the entire measuring point.
2. What is the function of the local magnetic display?
The local magnetic display is primarily used for immediate visual inspection at the vessel.
With a magnetic bypass indicator, no mechanical shaft moves directly from the float to the display. Instead, the magnetic field acts through the wall of the bypass chamber.
With the WIKA BNA, two-color rollers or magnetic flaps are mounted externally. As the float magnet passes, these display elements rotate and thereby indicate the current height of the liquid level.
The key advantage is that this display functions without an electrical power supply.
Even if the PLC fails, the power supply is interrupted or the 4–20 mA current loop is defective, an operator can still read the level directly at the vessel – provided that the bypass chamber, float and magnetic display are mechanically functioning correctly.
The local display therefore provides a valuable fallback level for servicing, commissioning and troubleshooting.
However, it does not automatically replace an independent second level sensor because it uses the same float as the externally mounted magnetic auxiliary sensors.
3. How is the float position converted into a remote signal?
For a PLC, process control system or data logger, a purely visual indication is not sufficient. The level must be converted into an electrical signal.
For this purpose, a level transmitter can be mounted externally on the bypass chamber.
This sensor also uses the magnetic field of the float. No additional opening in the pressure-bearing bypass chamber is therefore required.
The position is detected differently depending on the transmitter principle.
With a reed measuring transmitter, the float magnet sequentially actuates reed contacts within a resistor chain. The level is determined from the resulting resistance or voltage signal.
With a magnetostrictive transmitter, the float position is determined with high resolution through the interaction of the float magnetic field with a magnetostrictive sensing element.
The electronics can use this information to generate, for example, a 4–20 mA signal proportional to the configured level range.
The same physical level is therefore continuously available outside the immediate plant area.
4. How do additional magnetic switches work?
Magnetic switches perform a different task from the continuous level transmitter.
They are not intended to detect every intermediate value, but rather a defined limit level.
For example, one switch can be mounted at the height at which a MIN alarm is to be triggered. A second switch can be used as a MAX or overfill alarm.
When the magnetic field of the float reaches the configured switching range, the magnetic switch changes its electrical state.
The resulting binary signal can be transmitted directly to a control system, relay, alarm unit or suitable safety logic.
With bistable versions, the switching state reached can remain stored until the float passes the corresponding reset point.
A limit switch therefore does not represent a second continuous level measurement. It answers a much simpler but often very important operational question:
Has the defined limit level been reached – yes or no?
5. Direct comparison of local indication, transmitter and limit switches
| Information path | Output | Typical function | Electrical power supply required? |
|---|---|---|---|
| Magnetic display | Directly visible level height | Local inspection | No |
| Level transmitter | Continuous electrical measured value | PLC, control system, control, trend | Yes, depending on version |
| MIN magnetic switch | Binary limit signal | Dry-run protection, minimum inventory, alarm | Depending on switch and evaluation system |
| MAX magnetic switch | Binary limit signal | Overfill alarm, pump shutdown | Depending on switch and evaluation system |
The different signal types are precisely what makes this combination attractive.
An error in analog scaling, for example, does not necessarily affect the local indication. Likewise, a break in the 4–20 mA loop does not affect the purely magnetic local display.
Conversely, a jammed display strip can be identified if the transmitter continues to provide a plausible and changing measured value.
The three levels therefore enable effective diagnosis of different signal and display problems.
6. What does redundancy actually mean with a bypass indicator?
The term redundancy must be used carefully with this type of design.
From an information-processing perspective, several separate signal paths do indeed exist.
The local display requires neither a PLC nor an electrical power supply. The continuous transmitter has its own electrical signal path. The limit switches, in turn, operate independently of the transmitter’s analog scaling.
As a result, an individual electrical fault can often be detected or bypassed using another information path.
This characteristic can be described as functional or signal-path redundancy.
From a metrological perspective, however, the functions share a common basis: the liquid in the bypass chamber and the magnetic float inside it.
This creates a common source of failure that can affect several outputs simultaneously.
For normal process monitoring, servicing and plausibility checking, the combination is nevertheless extremely valuable. For applications requiring fully independent redundant level measurement, the overall architecture must be considered in greater detail.
7. Why the common float remains a common source of failure
Assume that the float becomes stuck at 60% level.
The magnetic display may then remain at 60%. An externally mounted reed or magnetostrictive transmitter continues to detect the position of the same magnet and also reports approximately 60%. A limit switch located above or below this point can likewise retain an apparently plausible state.
Three pieces of information therefore agree – even though the actual vessel level may meanwhile have changed significantly.
Similar behavior is possible if both process connections of the bypass indicator are isolated from the vessel by valves. The entire bypass system then only indicates the trapped condition within the bypass chamber.
These so-called common-cause failures are the main reason why the additional components must not be equated with three completely independent level measurements.
For plant design, a distinction must therefore be made between redundancy of the signal path and redundancy of the measuring principle.
8. When does the bypass level actually correspond to the vessel level?
The principle of communicating vessels only works if the vessel and bypass chamber are correctly connected hydraulically and pneumatically.
The lower connection must allow unrestricted liquid exchange. The necessary pressure equalization through the upper connection must also be ensured.
If either path is blocked, the level in the bypass may differ from the actual vessel level.
Typical causes include closed shut-off valves, deposits, solidified medium, contamination, foreign objects or unsuitable piping arrangements.
Trapped gas or liquid volumes can also interfere with equalization.
During troubleshooting, the electrical transmitter should therefore not be checked first in isolation. It must initially be confirmed that the bypass chamber is still physically reproducing the actual vessel level.
9. Why is the density of the medium decisive for the float?
The float is supported by hydrostatic buoyancy.
This buoyancy depends directly on the density of the medium. For this reason, a float is designed for a specific density range.
If the density changes significantly compared with the design value, the immersion depth of the float also changes.
This shifts the position of the magnet relative to the actual liquid surface.
With strongly changing process media or large temperature-related density variations, it should therefore be checked whether the float design is still suitable for the application.
For interface measurement, the situation is even more demanding because the float must be specifically matched to the densities of two different media.
The length of the magnetic display alone therefore does not indicate whether the selected float is suitable for the actual medium.
10. How temperature, viscosity and insulation influence the bypass
The bypass chamber is located outside the actual vessel. Its thermal condition can therefore differ from that of the process.
With hot media, the bypass may cool more strongly toward the surroundings. With cold or cryogenic media, heat can instead be transferred into the bypass from the environment.
This temperature change can in turn alter the viscosity and density of the medium.
With viscous products, the float may therefore move less freely inside the bypass than would be expected from the main vessel.
With crystallizing or solidifying media, the cross-section of the bypass chamber can additionally become obstructed.
Depending on the application, heating, heat tracing or insulation of the bypass system may therefore be required.
It must also be taken into account that not only the local indication but all attached magnetic measuring and switching functions remain dependent on free movement of the float.
11. Correctly define the measuring range and process connections
The mechanically visible range of a bypass indicator and the electrically configured measuring range must match the actual vessel geometry.
The positions of the upper and lower process connections are particularly important.
The safely usable float range is mechanically limited by the bypass chamber, the connections and the upper and lower stops.
A switching point should therefore not simply be positioned outside the hydraulically effective range.
With WIKA BGU magnetic switches, for example, it must be taken into account that reliable operation can only be ensured within the intended range between the process connections.
For plant planning, the actual vessel levels corresponding to 0%, 100%, MIN and MAX should therefore be defined before ordering.
Only then can the connection center distance, overall length, transmitter range and switch positions be determined correctly.
12. Correctly scale the 4–20 mA signal
The continuous remote measured value is frequently transmitted to the control system as a 4–20 mA signal.
It must be clearly defined which physical level height is represented by 4 mA and which height is represented by 20 mA.
This may sound obvious, but different reference points can quickly make the situation more complex in practice.
The mechanical scale may, for example, be specified in millimeters while the PLC displays 0 … 100% or vessel volume in liters.
Furthermore, linear level measurement is not automatically identical to vessel volume. In a horizontal cylindrical tank or a vessel with dished ends, there is a non-linear relationship between level height and volume.
The volume calculation must then be carried out in the higher-level evaluation system and must not be confused with the actual level measurement.
During commissioning, the 4–20 mA signal should therefore not only be checked electrically but also compared with the actual float position and local indication.
13. Selecting a reed or magnetostrictive transmitter
Different principles are available for continuous electrical detection on a magnetic bypass indicator.
With a reed measuring transmitter, the float position is detected by a chain of magnetically actuated reed contacts and resistors.
This design is robust and well suited to many conventional process applications. The spatial resolution is influenced, among other factors, by the contact pitch used.
Depending on the version, the WIKA BLR is available with different contact pitches. The resulting electrical information can be transmitted via suitable head-mounted transmitters, for example as a 4–20 mA or HART signal.
A magnetostrictive transmitter such as the WIKA BLM, by contrast, continuously determines the position using a transit-time measurement of a mechanical wave within the magnetostrictive sensing element.
This principle is particularly suitable when high position resolution or more precise continuous remote measurement is required.
| Characteristic | Reed measuring transmitter | Magnetostrictive transmitter |
|---|---|---|
| Position detection | Reed contacts and resistor chain | Magnetostrictive transit-time measurement |
| Resolution | Influenced by contact pitch | High continuous position resolution |
| Typical signal processing | Transmitter for e.g. 4–20 mA / HART | Direct electronic measured-value output |
| Common basis | Magnetic field of the bypass float | Magnetic field of the bypass float |
Even with different electrical measuring principles, the float therefore remains the common mechanical reference.
14. Using MIN and MAX switches effectively
In theory, an analog transmitter can already evaluate any desired level. Nevertheless, additional physical magnetic switches are useful in many installations.
One reason is the separation of signal paths.
The PLC can calculate a MAX alarm from a 4–20 mA signal. An additional magnetic switch, by contrast, generates a separate binary signal at a mechanically defined position.
This means that an error in analog scaling, the analog output, PLC channel parameterization or software logic is not automatically transferred to the limit contact.
Typical applications include minimum level, pump enable, dry-run protection, high-level alarm and overfill alarm.
After installation, the position of the switch should be checked using the actual float or a controlled level change.
Particularly with bistable switches, the switching and reset direction should also be documented.
15. Using three signal paths for plausibility checking
The greatest practical advantage of the combination arises when the signals are not merely displayed in parallel but actively compared with one another.
If the local magnetic display indicates 70%, for example, while the transmitter remains constant at 35%, there is clearly a deviation within the display or signal chain.
If the local display and transmitter both indicate 80%, while the MAX switch has not activated at its defined switching point, the limit switch or its wiring should be checked.
If, on the other hand, all three information paths remain unchanged even though the actual vessel content is known to have changed, this is more likely to indicate a common mechanical or hydraulic cause.
| Observation | Likely fault area | Recommended check |
|---|---|---|
| Local display moves, 4–20 mA remains constant | Transmitter, power supply, current loop or evaluation | Check transmitter output and PLC input |
| 4–20 mA changes, local display remains stationary | Magnetic display or display elements | Check flap/roller system |
| Display and transmitter agree, limit switch does not switch | Switch position, alignment, wiring or switch fault | Test switch using actual float movement |
| All signals remain stationary | Float blocked or bypass isolated from vessel | Check bypass connections, valves and float movement |
| All signals change but do not match the vessel | Density, bypass communication or incorrect process assignment | Check medium, float design and hydraulic connection |
| Constant difference between local and electrical indication | Zero/span scaling or mechanical alignment | Check reference points and transmitter configuration |
This type of signal diagnosis provides significantly more information than evaluating a single measured value in isolation.
16. When a second independent measuring principle is required
For normal process control, the combination of magnetic display, transmitter and limit switch can provide a very robust architecture.
However, it should not automatically be regarded as three completely independent level measurements.
If a protective function is so critical that a common failure of the bypass system is unacceptable, a second independent measuring principle must be considered.
This could be, for example, a separate radar measurement, hydrostatic measurement, differential-pressure measurement or another suitable point-level measuring principle.
The required concept depends on the risk assessment, plant design and, where applicable, functional-safety requirements.
The decisive factor is that an additional sensor should not merely provide a second electrical output, but should ideally have different common failure causes.
A radar probe installed in the vessel, for example, is not dependent on the mechanical float of the bypass indicator.
Especially for overfill protection or other safety-related functions, a distinction must therefore be made between an additional indication and a genuinely independent protection layer.
17. Systematically commissioning the measuring point
A combined bypass measuring point should be tested as a complete system during commissioning.
First, it should be checked whether the bypass chamber, process connections, shut-off valves and venting have been installed according to the plant design.
It should then be verified that the selected float is suitable for the density, temperature and pressure of the medium.
A controlled level change should then be performed. The local display must follow the float movement across the entire intended range.
At the same time, the continuous output signal is recorded. For 4–20 mA, zero point and span are compared with the defined mechanical reference heights.
The individual magnetic switches are then deliberately passed by the float. Switching point, switching state and reset behavior are compared with the PLC or alarm system.
Finally, it should be checked whether the visualization in the control system uses the same unit and reference range as the local measuring point.
This combined test creates reference values that are extremely useful during later maintenance and troubleshooting.
18. Systematically diagnosing typical fault patterns
In the event of a fault, the first step should be to determine which part of the measurement chain is actually affected.
A frozen PLC value does not automatically mean that the float is not moving. Conversely, a plausible local indication does not prove that the electrical transmitter has been scaled correctly.
Observing the signals over time is particularly important.
If an indication responds slowly to a process change, increased viscosity or a sluggish float may be the cause. If the transmitter suddenly jumps to an electrical error value, the problem is more likely to be related to the power supply or signal path.
If unusual deviations are detected after maintenance work, the positions of the upper and lower shut-off valves should also be checked.
A fully isolated bypass can provide a remarkably stable and plausible measured value – but it then only indicates the trapped level within its own chamber.
19. Suitable WIKA / KSR Kuebler level measurement technology from ICS Schneider
ICS Schneider Messtechnik offers bypass level indicators, continuous level transmitters, magnetic switches and floats from WIKA / KSR Kuebler. An overview can be found under Level Measurement Technology.
19.1 WIKA Model BNA Bypass Level Indicator
The WIKA model BNA combines a bypass chamber mounted on the side of the vessel with a magnetic float and an externally mounted magnetic display.
The level is therefore visible directly at the vessel without requiring an electrical power supply.
Depending on the specific version, applications from very low temperatures through to high-temperature and high-pressure processes are possible. WIKA specifies operating limits for the product family of up to −196 … +450 °C, from vacuum up to 400 bar, with float versions available from certain minimum densities.
These values represent maximum limits of the product family and must be checked separately for each specific combination of materials, pressure, temperature and float.
Transmitters and magnetic switches can optionally be added externally to the bypass.
19.2 WIKA Model BLR Reed Level Transmitter
The WIKA model BLR detects the level using magnetically actuated reed contacts within a resistor chain.
Different contact pitches are available depending on the version. Suitable transmitters can be used to generate field signals such as 4–20 mA or HART as well as other communication options.
The BLR is therefore suitable for robust continuous level measurement and conventional process-control technology.
19.3 WIKA Model BLM Magnetostrictive Level Transmitter
The WIKA model BLM uses a magnetostrictive measuring principle to determine the float position with high resolution.
The transmitter is mounted externally on the bypass and therefore also operates without an additional direct process connection.
The product family supports, among other options, 2-wire technology with a 4–20 mA signal and digital measured-value transmission.
The BLM is particularly suitable when finely resolved continuous level information is required for control, trend analysis or more precise remote indication.
19.4 WIKA Model BGU Magnetic Switch
The WIKA model BGU is used for limit-level detection on the bypass level indicator.
Depending on the version, the switches are mounted on the magnetic display or directly on the bypass chamber and adjusted to the required switching point.
They provide a binary signal for MIN, MAX, pump or alarm functions, for example.
Different switching functions, approvals and temperature ranges are available depending on the version.
When positioning the switch, care must be taken to ensure that it is mounted within the functional float range and that its orientation corresponds to the intended switching logic.
19.5 WIKA Model BFT Float
The float is the central mechanical element of the bypass system.
WIKA offers different BFT float versions depending on density, pressure, temperature and process medium.
Since the local display, continuous measurement and magnetic switches all use the magnetic field of this float, its correct design is decisive for the entire measuring point.
19.6 Application Engineering by ICS Schneider
For designing a magnetic bypass indicator, the most important information includes medium, minimum and maximum density, process pressure, process temperature, vessel connections, required center-to-center distance, measuring range, materials, connection arrangement, insulation or heating and required approvals.
For the electrical extension, the required output signal, resolution, communication interface and the number and function of the limit switches must also be specified.
It should also be clarified during the planning stage whether the additional signals are intended only for process monitoring and plausibility checking or whether genuinely independent protective measurement is required.
20. Conclusion
A magnetic bypass level indicator can perform significantly more functions than a purely mechanical level display.
The local magnetic display allows immediate inspection without an electrical power supply. An additional transmitter provides a continuous measured value for the PLC, control system or data recording. Magnetic switches can report fixed MIN and MAX limits independently of the analog scaling.
These different information paths can be compared with one another very effectively for plausibility checking.
If the local display moves while the 4–20 mA signal remains unchanged, the fault is probably located in the electrical measurement chain. If the local display and transmitter agree while a limit contact fails to respond, the switch can be investigated directly.
The combination therefore significantly improves diagnostic capability and plant availability.
However, it has a common mechanical basis. The bypass chamber and magnetic float affect all attached functions.
A blocked float or hydraulically isolated bypass chamber can therefore cause several apparently independent signal paths to become incorrect at the same time.
The term redundancy should therefore be used deliberately:
Local indication + continuous transmitter + limit switch = very good functional and signal-path redundancy, but not three completely independent level measurements.
If true measuring-principle redundancy is required, an additional measuring method independent of the bypass float must be provided.
For normal process applications, the following structure is useful:
Local indication for the operator → continuous signal for control and trending → separate limit switches for defined alarms → mutual plausibility checking → additional independent measuring principle for critical protective functions.
When correctly designed, the magnetic bypass indicator therefore combines good local readability, robust remote signal transmission and clearly defined limit alarms within a single process-compatible measuring point.
21. Frequently asked questions about bypass indicators with transmitters and switches
21.1 Does the local indication work without electrical power?
Yes. With a magnetic bypass indicator such as the WIKA BNA, the display is actuated by the magnetic field of the float and does not require an electrical power supply for purely local indication.
21.2 Can I use a transmitter and magnetic switches at the same time?
Yes. A bypass level indicator can be equipped with a continuous transmitter and additional magnetic switches.
21.3 Are local indication and the 4–20 mA signal independent?
The display and signal paths are partially independent. However, both functions normally use the same magnetic field of the common float and are therefore not completely independent from a metrological perspective.
21.4 Do two magnetic switches constitute redundant level measurement?
No. They provide two separate limit signals but still use the same float and bypass chamber as their common process information.
21.5 What happens if the float becomes stuck?
The magnetic display, transmitter and magnetic switches can all simultaneously indicate an unchanged condition even though the actual level in the vessel has changed.
21.6 Can a bypass indicator show an incorrect level even if all signals agree?
Yes. For example, the bypass chamber may be isolated from the vessel by closed or blocked process connections. All components may then indicate the same bypass level, but no longer the actual vessel level.
21.7 Why does the bypass require two vessel connections?
They allow the liquid level in the bypass chamber to equalize with the vessel level according to the principle of communicating vessels while also providing the required pressure equalization.
21.8 Why is liquid density important?
Density determines buoyancy and therefore the immersion depth of the float. The float must therefore be designed for the actual process density.
21.9 What is the difference between BLR and BLM?
The BLR uses reed contacts and a resistor chain. The BLM determines the float position magnetostrictively and provides high-resolution continuous position measurement.
21.10 Is a reed transmitter truly continuous?
It provides a continuously usable level signal, but the internal position detection is based on discrete reed contacts. The achievable resolution is therefore influenced, among other factors, by the contact pitch used.
21.11 When is a magnetostrictive transmitter useful?
A magnetostrictive transmitter can be advantageous when high position resolution, precise trend representation or finer continuous measurement is required.
21.12 Why use additional magnetic switches if 4–20 mA is already available?
A separate limit switch has its own electrical signal path and is independent of the analog scaling and the software limit derived from it. This can improve diagnostics and operational reliability.
21.13 Can a MAX switch be used as overfill protection?
This depends on the required safety function, the specific device approval and the overall safety architecture. A normal process limit switch does not automatically constitute a compliant independent overfill protection system merely because it is used as a MAX switch.
21.14 Where may a magnetic switch be mounted?
The switch must be positioned within the usable float range or the range specified by the manufacturer. For BGU switches, the area between the process connections must be taken into account in particular.
21.15 What does a bistable magnetic switch mean?
A bistable switch can retain its switching state after the float magnet has passed until the magnetic field again passes through the corresponding switching range in the opposite direction.
21.16 Can the 4–20 mA signal be scaled directly in liters?
This can be done in the higher-level evaluation system. However, with non-linear vessel geometries, the linear level height must not be converted directly into volume without using the vessel characteristic.
21.17 Why can the local indication and remote signal show different values?
Possible causes include incorrect transmitter scaling, mechanical displacement of the sensor, a blocked magnetic display or incorrect PLC configuration.
21.18 What should be checked during commissioning?
The bypass connection, float movement, local indication, 4–20 mA zero point and span, and all limit switches should be checked together across the actual intended level range.
21.19 When do I need an independent second measuring principle?
When a common failure of the bypass chamber or float is not acceptable for the relevant protective or process function. In such cases, an additional radar, hydrostatic or differential-pressure measurement may be appropriate.
21.20 What information does ICS Schneider require for system design?
Useful information includes medium, density range, viscosity, process pressure, process temperature, vessel connections, center-to-center distance, required measuring range, materials, number and position of limit switches, required output signal or communication protocol, hazardous-area requirements and information on whether the measuring point is intended only for process monitoring or also for a safety-related function.