Connecting a Temporary Pressure Sensor to MINIMESS: Planning the Measuring Range, Adapter and Cable Safely

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A hydraulic system shows sporadic faults, but the permanently installed pressure sensor provides only a single process value or is not located at the critical point. For troubleshooting purposes, an additional pressure sensor is therefore to be connected temporarily and the pressure profile recorded over several minutes, hours or load cycles.

If a MINIMESS test point is already available, such a measurement can often be implemented without modifying the actual hydraulic line. A suitable pressure sensor is connected to the service point via a direct connection or a microbore hose. After the measurement has been completed, the additional measuring equipment can be removed again.

However, the mechanical connection alone is not sufficient. For a reliable temporary pressure measurement, the MINIMESS series, sensor connection, pressure range, permissible pressure peaks, hose, medium, temperature, electrical supply, sampling rate and secure mounting must all be compatible.

Especially when searching for short pressure peaks, the measuring chain itself can become the limiting factor. A fast pressure sensor will not provide a useful peak-pressure measurement if a long measuring hose containing trapped air is used or if the data logger records too slowly.

Suitable components can be found at ICS Schneider under MINIMESS couplings and hoses. Suitable sensors can be found under pressure sensors and differential pressure sensors.

Why MINIMESS is suitable for temporary pressure measurements

MINIMESS test points provide permanent access to a fluid system. Instead of opening a hydraulic line for every diagnostic task, a suitable measuring instrument can be connected via the existing test coupling.

Typical applications include:

• temporary pressure measurements,
• troubleshooting pumps and valves,
• comparison measurements with permanently installed sensors,
• recording load cycles,
• condition monitoring,
• commissioning and maintenance.

The principle is particularly practical because the actual process connection remains permanently installed in the system. When the coupling is connected, the integrated shut-off element of the test point is opened. After uncoupling, the measuring point closes again.

This makes it possible to temporarily set up an additional measuring chain consisting, for example, of:

MINIMESS test point → measuring hose → pressure sensor → measuring cable → data logger

on the system.

However, one important point must be observed: Only the MINIMESS coupling connection specifically designed for this purpose may be operated under pressure in accordance with its specification. Normal threaded adapters, fittings or sensor connections must not be loosened while the system is under pressure.

First identify the existing MINIMESS measuring point

Before selecting the sensor or hose, it should first be determined which test point is actually installed on the machine.

The statement “there is a MINIMESS connection” is not sufficient.

The following should be checked in particular:

• MINIMESS series,
• coupling thread,
• maximum permissible operating pressure,
• seal material,
• medium,
• medium temperature,
• condition of the test point.

For older machines, components should not be ordered based solely on visual appearance. Different test points may look similar but use different coupling threads.

Particularly helpful are:

• machine documentation,
• type designation of the test point,
• thread dimensions,
• a clearly recognizable photo,
• information from the machine manufacturer, if available.

Do not confuse MINIMESS 1620, 1615 and 1215

MINIMESS does not refer to a single connection thread. Different series are available.

For commonly used versions, the coupling threads differ, for example:

Series	Coupling thread	Typical application
MINIMESS 1620	M16 × 2	Very common standard series for hydraulic and service applications
MINIMESS 1615	M16 × 1.5	Alternative series for similar applications
MINIMESS 1215	M12 × 1.5	Compact version for limited installation space

An M16×2 connection and an M16×1.5 connection differ only in their thread pitch. They can therefore easily be confused at first glance.

An incompatible coupling thread must never be forced onto the test point.

Damaged threads or sealing surfaces can quickly turn a simple diagnostic task into a hydraulic system leak.

Typical setup for a temporary pressure measurement

Several configurations can be used for temporary pressure recording.

Option 1: Sensor directly on the test point

A suitable pressure sensor is connected directly to the test point using a MINIMESS direct connection.

Advantages:

• very small additional fluid volume,
• short hydraulic transmission path,
• favorable for rapid pressure changes.

Disadvantages may include limited installation space, vibration and mechanical loading of the test point.

Option 2: Sensor connected via a microbore hose

A MINIMESS measuring hose is installed between the test point and the sensor.

Advantages:

• the sensor can be mounted in an easily accessible location,
• less direct mechanical loading from the machine,
• measurements can be performed at hard-to-reach test points,
• the measuring instrument and sensor can be positioned more conveniently.

The hose then becomes part of the measuring chain and can influence its dynamic behavior in particular.

Option 3: Mobile multi-channel measuring system

For more extensive diagnostic tasks, a mobile measuring system can be used to which one or more pressure sensors are connected.

This allows simultaneous recording and comparison over time of, for example:

• pump pressure,
• working pressure,
• control pressure,
• pressure upstream and downstream of a filter.

Especially for sporadic faults, simultaneous comparison of several pressure points is often considerably more informative than several individual measurements performed one after another.

Selecting the correct pressure range for the sensor

The sensor measuring range should not be selected solely on the basis of normal operating pressure.

Example:

A machine operates at 210 bar under normal conditions. During rapid valve switching, however, significantly higher pressure peaks may occur.

A sensor whose measuring range ends only slightly above 210 bar may therefore be unsuitable.

At minimum, the following should be known when selecting the sensor:

• normal operating pressure,
• minimum expected pressure,
• maximum expected operating pressure,
• possible dynamic pressure peaks,
• sensor overload limit.

On the other hand, the measuring range should not be unnecessarily large.

If, for example, a control circuit operates between 0 and 25 bar, a 0…600 bar sensor is generally not a sensible choice for accurately investigating small pressure changes.

The basic rule is:

As small as reasonably possible from a measurement perspective, but large enough to cover the actual maximum pressure including relevant pressure peaks.

The overload capability of the sensor is not an extension of its normal measuring range. A sensor should not intentionally be operated outside its specified measuring range merely because a higher overload limit is stated.

Considering pressure peaks and overload capability

Hydraulic systems can generate very short pressure events that are barely visible on a conventional pressure gauge.

Typical causes include:

• rapid closing of a valve,
• switching of directional control valves,
• load changes,
• moving against a mechanical stop,
• oscillating pressure control,
• unstable pressure relief valves.

Such a peak can be significantly higher than the apparently stable pressure value of the machine.

For sensor selection, this means:

1. Determine the known operating pressure.
2. Consider possible dynamic events.
3. Define the sensor measuring range.
4. Check the permissible overload pressure.
5. Select the recording rate to match the expected event duration.

However, a larger measuring range does not automatically protect the entire measuring system. The MINIMESS test point, hose, adapter and all fittings must also be suitable for the pressure that can occur.

Combining adapters and sensor process connections correctly

Many industrial pressure sensors do not have a MINIMESS direct connection, but instead use a process connection such as G 1/4.

A suitable adapter is then required.

A typical setup may, for example, be:

MINIMESS 1620 → suitable coupling or measuring hose → G 1/4 connection → pressure sensor

When using a hose assembly, the sensor end can already be fitted with a suitable connector.

Before ordering, the following points should be clearly defined:

• MINIMESS series on the machine side,
• pressure sensor thread,
• male or female thread,
• sealing principle,
• permissible pressure,
• material,
• media compatibility.

The thread alone is not enough

The fact that two components can mechanically be screwed together does not automatically mean that their sealing principles are compatible.

With parallel G threads, for example, sealing does not necessarily take place through the thread itself. Depending on the specific design, profile seals, flat gaskets or other defined sealing surfaces may be used.

The complete connection design should therefore always be considered rather than just the designation “G 1/4”.

Keep the adapter chain as short as possible

Several adapters screwed together in series are not necessarily technically incorrect. However, they increase:

• the number of potential leak points,
• the mechanical installation length,
• the leverage applied to the test point,
• the additional fluid volume.

Where possible, a properly configured connection with as few transitions as possible is therefore preferable.

Direct connection or microbore hose?

Whether the sensor should be connected directly to the measuring point or via a hose depends on the measurement task.

Criterion	Direct connection	Microbore hose
Hydraulic volume	Very small	Larger and dependent on length and internal diameter
Dynamic measurement	Generally favorable	Influence of the line must be considered
Accessibility	Sensor directly at the test point	Sensor can be positioned remotely
Vibration	Sensor directly exposed to machine vibration	Decoupled mounting possible
Installation space	Can be problematic	Flexible positioning
Service	Few components	Very flexible for diagnostics

For slowly changing operating pressures, the influence of a suitable measuring hose is often small.

However, if fast pressure peaks are to be investigated, the hydraulic connection should deliberately be kept as compact and well-defined as possible.

How hose volume and line length influence the measurement

A measuring hose is not an ideally rigid transmission element.

During a pressure change, the following factors act, among others:

• compressibility of the medium,
• elastic expansion of the hose,
• flow resistance of the microbore,
• any trapped gas bubbles.

The hydraulic connection can therefore influence the dynamic measurement signal.

Particularly critical are:

• very long hoses,
• very small cross-sections,
• trapped air,
• high-frequency pressure pulsations.

This does not mean that microbore hoses are generally unsuitable for dynamic measurements. Their small fluid volume is an important advantage, especially for measurement and service applications.

When searching for very short pressure peaks, however, the complete transmission path must be considered.

The usable dynamics of a measuring chain are not determined by the pressure sensor alone.

Avoiding air in the measuring hose

Trapped air is particularly unfavorable when measuring hydraulic pressure in a liquid-filled system.

Hydraulic oil is only slightly compressible compared with air. A gas bubble therefore acts as an additional elastic volume.

Possible effects include:

• delayed pressure transmission,
• damping of short pressure peaks,
• changed oscillation behavior,
• poorer reproducibility of dynamic measurements.

If the measuring setup needs to be vented, this should only be performed in accordance with the specified procedure.

A pressurized fitting must never simply be loosened to “let some air out”.

At high hydraulic pressures, escaping fluid can cause serious injuries.

For dynamic comparison measurements, the same hose configuration should also be used wherever possible. Different hose lengths or different amounts of trapped air can otherwise create apparent differences between two measuring points.

Checking medium, temperature and seals

Not every MINIMESS hose, seal and pressure sensor is suitable for every medium.

Before connection, the following should therefore be checked at minimum:

• hydraulic oil or other medium,
• medium temperature,
• ambient temperature,
• seal materials,
• hose material,
• sensor materials.

Material compatibility should be checked explicitly, especially with:

• water-glycol mixtures,
• fuels,
• aggressive liquids,
• thermal oils,
• high temperatures.

Even if the pressure range is suitable, an incorrect seal can be damaged by the medium or temperature.

The maximum permissible operating conditions of the complete measuring chain are determined by the component with the most restrictive limits.

4–20 mA, measuring instrument or data logger?

Once the hydraulic connection has been established, it must be decided how the sensor signal is to be recorded.

4–20 mA pressure sensor

A pressure sensor with a 4–20 mA output can generally be connected to a suitable data acquisition system, such as:

• a data logger with current input,
• a PLC,
• a mobile measuring instrument,
• a multi-channel measuring system.

One particular advantage of the current signal is its robust transmission even over longer cable distances.

For temporary measurement, however, supply voltage, input type, pin assignment and scaling must be configured correctly.

Sensor with system-specific recognition

With certain combinations of sensors and measuring instruments, additional sensor data can be recognized automatically by the measuring instrument.

This can simplify mobile servicing because, for example, the scaling associated with the sensor does not have to be entered manually each time it is used.

However, actual compatibility between the sensor and measuring instrument must be checked. The presence of a 4–20 mA output does not automatically mean that every additional digital sensor recognition function is supported by every measuring instrument.

Mobile multi-channel measuring instrument

A mobile multi-channel instrument is particularly practical for more extensive diagnostic tasks.

It allows several pressure signals and other process variables to be recorded and stored simultaneously.

This is particularly useful for:

• pressure peak analysis,
• comparison of several hydraulic circuits,
• longer-term data recording,
• service work on different machines.

Individual digital pressure gauge

For a simple local check, a digital pressure gauge may be sufficient.

However, when investigating a fault that occurs only sporadically, continuous recording is usually much more informative.

Matching the sampling rate to the pressure event

A common mistake in temporary pressure measurements is combining a fast pressure sensor with data acquisition that is too slow.

Example:

A pressure surge lasts only 5 ms, but the data logger stores only one measured value per second.

There is a high probability that the pressure peak will not appear in the recording at all.

Before the measurement, the following question should therefore be asked:

How fast is the event I am trying to detect?

Measurement task	Required consideration
Slow pressure drift over several hours	A low sampling rate may be sufficient
Pump cycle lasting several seconds	Several measured values per cycle are required
Fast valve switching	A significantly higher sampling rate is required
Short hydraulic pressure surge	Highly dynamic measuring chain and fast recording required

The sensor, hydraulic connection, measuring instrument and storage interval must therefore all be matched to the measurement task.

A high internal sampling rate of the measuring instrument is only useful if the connected sensor and hydraulic measuring path can also transmit the dynamics being investigated.

Planning measuring cables and electrical supply correctly

For an electronic pressure sensor, the electrical side also forms part of the measuring chain.

The following should be checked:

• sensor supply voltage,
• pin assignment,
• connector type,
• signal type,
• current or voltage input of the measuring instrument,
• permissible load resistance for current signals,
• cable length,
• shielding and EMC requirements.

In a two-wire current loop, sufficient supply voltage must be available for the sensor, cable resistance and input resistance of the measuring instrument.

For a 4–20 mA sensor, the maximum available external load can be estimated approximately from:

Rload,max = (Usupply − Usensor,min) / 0.02 A

.

The actual permissible values must always be taken from the technical data of the sensor being used.

On machines with frequency converters, high-power motor cables or rapidly switched solenoid valves, careful cable routing should also be ensured.

Where possible, measuring cables should not be routed unnecessarily parallel to power cables. Shielding and grounding should be implemented in accordance with the specifications of the measuring system.

Mounting the sensor and hose securely

A temporary sensor is often required for only a few hours. Nevertheless, it should not be left hanging loosely from the machine.

Potential problems include:

• vibration,
• tension on the measuring hose,
• oscillating sensors,
• contact with hot components,
• pinch points,
• moving machine parts.

A sensor fitted with an adapter can exert considerable leverage on a small test point.

On strongly vibrating systems, it is therefore often preferable to connect the sensor via a short measuring hose and mount it separately.

The hose should be routed so that:

• no impermissible tensile load occurs,
• the minimum bend radius is maintained,
• no kinks occur,
• there are no chafing points,
• hot surfaces are avoided,
• sufficient clearance from moving components is maintained.

Avoiding leakage and contamination

A temporary measurement should not introduce a new fault into the system.

The test point and coupling should therefore be clean before connection.

Dirt particles on the coupling can:

• damage sealing surfaces,
• enter the hydraulic system,
• impair the shut-off element.

Before each measurement, the following should also be inspected:

• condition of the hose,
• damage to fittings,
• seals,
• threads,
• permissible operating pressure.

After coupling, the measuring point should be checked for visible leakage.

A leak in a high-pressure hydraulic system must never be searched for by hand. A fine jet of fluid can penetrate the skin and cause serious injury.

Ending the measurement safely and removing the sensor

Uncoupling must also be planned.

A suitable MINIMESS test point may be designed for defined coupling and uncoupling under operating pressure. Nevertheless, pressure and medium may remain trapped in the connected measuring hose and sensor after disconnection.

After completing the measurement, the following procedure should therefore be followed:

1. stop the recording,
2. disconnect the electrical connection in accordance with the measuring system,
3. disconnect the MINIMESS connection according to the manufacturer’s instructions,
4. relieve any trapped residual pressure only through an appropriate device,
5. check the test point for leakage,
6. reinstall the protective cap.

Threaded fittings on the hose or sensor must not be used to deliberately “bleed off” trapped pressure.

Before dismantling the measuring chain, it must be ensured that it is depressurized.

Typical fault patterns in temporary MINIMESS pressure measurements

Observation	Possible cause	Recommended check
Sensor cannot be coupled to the test point	Incorrect MINIMESS series or incorrect coupling thread	Clearly identify 1620, 1615 or 1215
Measured value remains at the upper end of the measuring range under load	Sensor measuring range too small	Check maximum pressure and pressure peaks
Small pressure changes are barely visible	Sensor measuring range unnecessarily large	Select an appropriate measuring range for the process
Pressure peaks are missing from the recording	Sampling rate too low or hydraulic connection too heavily damped	Check logger sampling rate, hose length and amount of trapped air
Measured value responds unusually slowly	Long microbore hose or gas bubble in the measuring path	Check the hydraulic setup
Electrical measurement signal jumps	Contact problem, unsuitable power supply or EMC interference	Check cable, connector, supply and cable routing
4–20 mA signal does not reach the expected full-scale value	Loop resistance too high, incorrect supply voltage or incorrect scaling	Check supply voltage, total resistance and measuring instrument settings
Oil leaks after connection	Damaged seal, incorrect coupling or contaminated sealing surface	Stop the measurement safely and inspect the components
Temporary sensor shows a different value from the permanently installed sensor	Different measuring positions, ranges, calibration or process dynamics	Systematically compare the measuring points and measuring chains
Sensor or adapter vibrates strongly at the measuring point	Mechanically unfavorable direct installation	Consider using a short measuring hose and separate sensor mounting

Systematic procedure for temporary pressure measurement

A structured setup prevents incorrect measurements and unnecessary adapter combinations.

1. Define the measurement task: Which fault or pressure profile is to be investigated?
2. Select the measuring point: Is the existing MINIMESS connection hydraulically located at the correct point?
3. Identify the MINIMESS series: For example 1620, 1615 or 1215.
4. Record process data: Operating pressure, maximum pressure, temperature and medium.
5. Define the sensor range: Sufficient for operating pressure and relevant pressure peaks.
6. Define the dynamics: How short is the expected event?
7. Select direct connection or hose: Consider installation space, vibration and required dynamics.
8. Define the adapter: Clearly specify the MINIMESS side and sensor process connection.
9. Check the electrical signal: 4–20 mA, voltage signal or system-specific sensor interface.
10. Set the sampling rate: Match it to the event being investigated.
11. Secure the measuring chain: Protect the hose and cable against tension, chafing and moving parts.
12. Connect the measuring point: In accordance with the manufacturer’s instructions and safety requirements.
13. Perform a plausibility check: Does the stationary pressure correspond to the expected value?
14. Record the measurement: Capture the relevant machine cycle completely.
15. Evaluate the data: Compare mean value, min./max., peaks and temporal relationships.
16. Remove the measuring chain safely: Consider residual pressure and reinstall the protective cap.

Practical example: sporadic pressure drops on a hydraulic machine

A production machine normally operates at a hydraulic pressure of approximately 180 bar. Several times per shift, however, the feed movement briefly drops out.

The permanently installed pressure sensor is evaluated by the PLC with a relatively slow process sampling rate. No clear pressure drop can be identified in the existing trend data.

Step 1: Use the existing service point

A MINIMESS test point is located near the affected valve block.

The series is clearly identified using the system documentation or the existing coupling.

Step 2: Select a suitable pressure sensor

The normal pressure is 180 bar, while higher dynamic values may occur. A pressure sensor is selected so that both operating pressure and expected peaks remain within its specified measuring range.

Step 3: Define the measuring setup

Because the test point is located in an area subject to strong vibration, the sensor is not mounted directly at the measuring point using a long rigid chain of adapters.

Instead, a short suitable MINIMESS microbore hose is used and the sensor is mounted in a mechanically protected position on the machine frame.

Step 4: Fast recording

The pressure sensor is connected to a suitable mobile multi-channel measuring system and recorded at a significantly higher sampling rate than the existing PLC trend signal.

Step 5: Capture the fault event

During one machine cycle, a very short pressure drop becomes visible. The pressure at the investigated measuring point falls sharply for a brief moment and then recovers immediately.

This event was practically invisible in the slowly recorded PLC trend.

Step 6: Add a second measuring point

The pump pressure is simultaneously measured via another existing MINIMESS test point.

The recording shows:

• pump pressure remains stable,
• pressure downstream of the affected valve briefly drops.

The troubleshooting area can therefore be narrowed down to the section between the two measuring points.

Result: The additional pressure sensor was required only for diagnostics. Thanks to the existing MINIMESS service points, the measurement could be carried out without permanently modifying the hydraulic line.

The example also shows why the measuring point, sensor range, hydraulic connection and data logger must be considered together.

Suitable MINIMESS and HySense products for temporary pressure measurements

MINIMESS 1620 – test point for hydraulic and service applications

The MINIMESS 1620 test point is a widely used version for measuring, testing and servicing fluid systems.

The series uses an M16 × 2 coupling thread and, depending on the version, is designed for operating pressures up to 630 bar.

Using a suitable connection, the following can be temporarily connected to the system:

• measuring hoses,
• pressure sensors,
• pressure gauges,
• test instruments.

The test point allows the intended connection side to be coupled even while the system is pressurized. The applicable operating limits and correct coupling design must always be observed.

Further information can be found under MINIMESS 1620 at ICS Schneider.

MINIMESS microbore hoses – flexibly connecting the sensor to the measuring point

MINIMESS hoses are specifically intended for measuring and service connections and are available, among others, in DN2 and DN4.

Depending on the version, different:

• working pressures,
• hose materials,
• lengths,
• fittings,
• sensor connections

can be implemented.

For the versions offered by ICS, maximum operating pressures range, depending on the hose version, from 400 to 630 bar for DN2 and from 315 to 450 bar for DN4.

This allows, for example, a suitable MINIMESS coupling to be selected on the machine side and a connection matching the pressure sensor on the sensor side.

The low fluid volume of the microbore line is particularly useful for temporary pressure measurements.

Further information can be found under MINIMESS hoses at ICS Schneider.

HySense PR509 – 4–20 mA pressure sensor for fast pressure measurements

The HySense PR509 is a piezoresistive pressure sensor with a 4–20 mA output and a mechanical G 1/4 connection according to ISO 228.

Its features also include:

• cable with M16 × 0.75 circular connector,
• short response time,
• ISDS sensor recognition when used with compatible Hydrotechnik measuring instruments of the MH20xx series.

For temporary MINIMESS measurement, the G 1/4 process connection can be connected to the test point using a suitable MINIMESS direct adapter or an appropriately configured measuring hose.

The sensor is particularly suitable where an analog 4–20 mA pressure signal with good dynamic response is required.

Important: Automatic ISDS sensor recognition is an additional system-specific function. When using another measuring instrument with a 4–20 mA input, the electrical connection and scaling must be configured according to the measuring system used.

Further information can be found under HySense PR509 at ICS Schneider.

HySense PR130 I5 – universal sensor with M12 connection

The HySense PR130 I5 is also suitable for conventional industrial pressure measurements.

Depending on the version, the sensor offers:

• 4–20 mA or 0–10 VDC output signal,
• M12 × 1, 4-pin electrical connection,
• ISO 228-G 1/4 mechanical connection,
• IP67 degree of protection.

The M12 connection is particularly practical for temporary measuring setups and permanently prepared measurement points because pre-assembled measuring cables can be connected easily.

For connection to a MINIMESS test point, a hydraulic connection suitable for both the G 1/4 process connection and the existing MINIMESS series is required.

When using the 4–20 mA signal, the sensor can be combined with a suitable PLC, data logger or mobile measuring system with the appropriate current input.

Further information can be found under HySense PR130 I5 at ICS Schneider.

HySense PR101 – pressure sensor with MINIMESS 1620 direct connection

If as little mechanical adaptation as possible is required, a sensor with a direct MINIMESS connection can be advantageous.

The HySense PR101 features a mechanical MINIMESS direct connection of the 1620 series.

Technical features include:

• piezoresistive measuring principle,
• gauge pressure measurement,
• measuring range up to 0…600 bar in the listed version,
• 0…20 mA output signal,
• 6-pin Amphenol instrument connector,
• IP65 degree of protection.

The direct 1620 connection can eliminate an additional hydraulic adapter.

However, when selecting the sensor, it must be taken into account that the PR101 uses a 0…20 mA signal. The connected measuring instrument must support or correctly scale this signal.

Further information can be found under HySense PR101 at ICS Schneider.

MultiSystem 5070 – mobile recording of several pressure profiles

If more than a single instantaneous pressure value is required and several pressure profiles need to be analyzed simultaneously, the MultiSystem 5070 can be used.

The mobile measuring system offers, among other features:

• several analog measuring inputs,
• signal inputs for 0/4…20 mA and various voltage signals,
• additional digital or calculated channels,
• recording of measurement series,
• sampling rates up to 10 kHz,
• USB, RS232 and CAN interfaces.

This makes the instrument particularly suitable for diagnostic tasks in which, for example, pump pressure and consumer pressure need to be recorded simultaneously and compared later.

When combining the instrument with an analog pressure sensor, the signal type, connecting cable, supply and scaling must match the specific sensor version.

Further information can be found under MultiSystem 5070 at ICS Schneider.

Which combination is suitable for the measurement task?

Measurement task	Suitable combination
Simple operating pressure measurement at an existing test point	MINIMESS + suitable pressure gauge or pressure sensor
Temporary measurement with 4–20 mA signal	MINIMESS + hose/direct adapter + HySense PR509 or PR130 I5
Minimum hydraulic adaptation on MINIMESS 1620	HySense PR101 with MINIMESS 1620 direct connection
Investigating pressure peaks	Short hydraulic measuring path + fast pressure sensor + fast data acquisition
Comparing two or more pressure points	Several pressure sensors + MultiSystem 5070
Long-term recording for condition monitoring	Pressure sensor + suitable data acquisition system with appropriate storage interval

An overview of all service components can be found under MINIMESS couplings and hoses at ICS Schneider.

Conclusion

An existing MINIMESS test point is a very practical way of temporarily using an additional pressure sensor on a hydraulic system. For troubleshooting and condition monitoring, an additional measuring point can therefore be used without permanently modifying the actual pipe or hose line.

However, correct design of the complete measuring chain is essential.

First, the MINIMESS series must be clearly identified. M16×2, M16×1.5 and M12×1.5 are not interchangeable.

The pressure sensor should then be selected so that its measuring range and overload capability are suitable for the actual system pressure including relevant pressure peaks. An unnecessarily large measuring range, on the other hand, is often unfavorable when investigating small pressure changes.

For the mechanical connection, a choice must be made between a direct connection and a microbore hose. A hose simplifies installation and mechanical decoupling, but for fast measurements it becomes part of the dynamic system itself. Length, internal volume and, in particular, trapped air can influence short pressure events.

With electronic sensors, the supply, measurement signal, cable and data logger must also be compatible. High sensor dynamics are of no benefit if the recording system is too slow.

For reliable diagnostics, the following therefore applies:

Consider measuring point → MINIMESS series → pressure range → adapter/hose → sensor → cable → measuring instrument → sampling rate as one complete measuring chain.

Safe handling is equally important. Only the MINIMESS coupling designed for this purpose may be operated under pressure in accordance with its specification. Threaded adapters and sensor fittings must not be loosened under pressure, and any residual pressure trapped in the measuring hose must be relieved in a controlled manner before dismantling the measuring chain.

FAQ: Temporarily connecting a pressure sensor via MINIMESS

Can a pressure sensor be connected directly to a MINIMESS connection?

Yes, provided that the sensor and MINIMESS series can be connected using a suitable direct connection. Alternatively, a microbore hose with a connection fitting suitable for the sensor can be used.

Can any pressure sensor be used with MINIMESS?

No. Pressure range, overload capability, process connection, medium, temperature and electrical interface must all be suitable for the application. A mechanically and pressure-rated adapter is also required.

What is MINIMESS 1620?

MINIMESS 1620 is a widely used series of test and service connections. The coupling thread is M16 × 2. Depending on the version, applications up to 630 bar are possible.

Is MINIMESS 1615 the same as MINIMESS 1620?

No. The 1615 series uses an M16 × 1.5 coupling thread, while the 1620 series uses M16 × 2. Despite their similar dimensions, the couplings must not be confused.

Which thread does MINIMESS 1215 use?

The 1215 series uses an M12 × 1.5 coupling thread and is more compact than the 16 mm series.

Can MINIMESS be coupled while under pressure?

Suitable MINIMESS test points are designed for defined coupling while the system is pressurized. However, the permissible operating conditions as well as the manufacturer’s instructions and safety requirements must always be observed.

Can I loosen a normal threaded adapter while it is under pressure?

No. The ability to connect or disconnect under pressure applies only to the MINIMESS connection specifically designed for this purpose. Normal threaded connections, sensor connections and adapters must not be loosened under pressure.

How do I select the correct pressure range for the pressure sensor?

The measuring range must cover the normal operating pressure and relevant pressure peaks. At the same time, it should not be unnecessarily large if small pressure changes need to be investigated accurately.

Should I use a 250 bar sensor for an operating pressure of 200 bar?

This may be suitable, but it must be checked against the actual possible maximum pressure and the permissible overload of the specific sensor. If dynamic peaks significantly above 250 bar can occur, a larger measuring range may be required.

Is the overload limit the same as the measuring range?

No. The overload limit describes an additional load limit of the sensor and is not an extended normal measuring range.

Why is a MINIMESS microbore hose used?

A microbore hose provides a flexible connection between the test point and measuring instrument while adding comparatively little fluid volume. This allows the sensor to be positioned away from a poorly accessible or highly vibrating area.

Does a long measuring hose influence pressure measurement?

For slow pressure changes, the influence may be small. For fast pressure surges and pulsations, hose length, hose volume, elasticity and trapped gas bubbles can influence the dynamic behavior of the measuring chain.

Why is air in the measuring hose problematic?

Air is significantly more compressible than hydraulic fluid. A gas bubble can therefore damp or delay pressure changes and, in particular, distort short pressure peaks.

Can I slightly loosen a fitting to vent the system?

Not while the system is pressurized. Venting and pressure relief must only be carried out using the specified procedure or appropriate equipment.

Which is better: mounting the sensor directly on MINIMESS or using a hose?

A direct connection provides a very short hydraulic measuring path. A hose, on the other hand, offers greater flexibility and can mechanically isolate the sensor from vibration. The better solution depends on installation space, dynamics and the measurement task.

Which current sensor is suitable for 4–20 mA measurement via MINIMESS?

For example, the HySense PR509 or HySense PR130 I5 can be used if the pressure range and operating conditions are suitable for the application. Both feature a G 1/4 process connection and can be connected via a suitable MINIMESS adapter or appropriately configured measuring hose.

Is there a pressure sensor with a direct MINIMESS 1620 connection?

The HySense PR101 features a mechanical direct MINIMESS connection of the 1620 series. This can eliminate one additional hydraulic adapter point. Its 0…20 mA output signal must be taken into account.

Can a 4–20 mA pressure sensor be connected to a data logger?

Yes, provided that the data logger has a suitable current input and the sensor supply, load resistance and electrical connections are correctly designed.

Why does a 4–20 mA sensor indicate an incorrect value even though the pressure is correct?

Possible causes include incorrect scaling, unsuitable supply voltage, excessive loop resistance, wiring errors or an incorrectly configured measuring range in the data logger.

How fast does the data logger need to measure?

This depends on the event being investigated. A much lower sampling rate is sufficient for slow pressure trends than for fast valve switching or pressure peaks lasting only milliseconds.

Can a slow data logger capture pressure peaks?

Only if the peak lasts long enough to be captured within the sampling interval. Very short pressure events may be missed completely if the sampling rate is too low.

Can I record two MINIMESS measuring points simultaneously?

Yes. Using two suitable pressure sensors and a multi-channel measuring system, pump pressure and consumer pressure, for example, can be recorded simultaneously. This can significantly improve troubleshooting.

Which measuring instrument is suitable for several pressure channels?

For mobile multi-channel measurements, the MultiSystem 5070 can be used, for example. It has several sensor inputs and allows different measured variables to be recorded and stored simultaneously.

Why does the temporary sensor show a different pressure from the permanently installed sensor?

The two sensors may be located at different hydraulic positions. In addition, their measuring ranges, accuracy, dynamics, calibration and recording rates may differ. It should therefore first be checked whether the same process pressure is actually being compared.

Does the temporary pressure sensor need to be secured?

On machines with vibration or moving components, the sensor should be mounted securely. A heavy sensor should not be allowed to oscillate directly on a small test point through a long rigid adapter chain.

What must be considered after the measurement?

The MINIMESS connection is disconnected in accordance with the specified procedure. It must then be considered that residual pressure may still be trapped inside the hose or sensor. Before dismantling the measuring chain, this pressure must be relieved in a controlled manner using an appropriate device.