Monitoring the bladder accumulator of a hydraulic system with moneo RTM

Industry 4.0

IIoT platform moneo

Monitoring and maintenance

Machine performance

Use Case

Bladder accumulators - like diaphragm, piston or spring accumulators- are hydraulic accumulators. In a hydraulic system, a bladder accumulator ensures volume compensation and energy storage and dampens pulsations.

moneo RTM ensures easy monitoring of bladder accumulators in hydraulic systems. Potential bladder failures or ruptures can be detected early and sudden downtimes of the hydraulic system can be prevented.

The starting position

Currently, the function of the bladder accumulator is not monitored. Maintenance activities are performed based on a set time interval. No information is available regarding the fatigue life of the bladder. The data of the existing pressure and temperature sensors is not analysed or monitored further.

This is why failures of the accumulator bladder are detected too late or aren’t detected at all. Damage to other system components can occur as a result. If volume compensation through the bladder accumulator is no longer ensured, the hydraulic pump will be subjected to an increased load, which means that it may no longer be possible to guarantee sufficient pressure energy.

Goal of the project

The condition monitoring method patented by ifm for this application helps to optimise maintenance and detect impending bladder failures at an early stage.

To detect a bladder failure in time, key parameters of the bladder accumulator must be monitored, such as the number of filling and draining operations. An alarm is to be triggered when a set threshold is exceeded.

The current condition of the bladder can also be detected by permanently measuring the surface temperature at various positions of the bladder accumulator, enabling early detection of a potential bladder failure/rupture.

Implementation

To achieve condition monitoring of the bladder accumulator, the existing sensors are used and the data and thresholds are visualised and managed in moneoRTM. Additional temperature bolt-on sensors are installed without having to intervene in the system. moneoRTM is installed on an internal server. Using an IO-Link master, all sensor values are transmitted to the internal VLAN and to moneo.

Success

With the help of moneo, it was able to implement condition-based maintenance and ensure the process capability of the hydraulic system. moneoRTM

visualises all measured values in a dashboard
calculates temperature differences between the temperature sensors
counts the number of filling and emptying operations of the bladder
allows threshold management
alerts via tickets, emails and SFI
ensures early detection of bladder ruptures
enables process optimisation from time-based to condition-based maintenance
enables monitoring of process values using AI methods

System structure

Pressure sensor system pressure
Temperature sensor hydraulic system
Temperature sensor accumulator
Temperature sensor bladder
IO-Link master

Dashboard

The visualisation dashboard provides users with a clear view of all relevant bladder accumulator data.

Temperature difference ③ and ④
Temperature difference ④ and ⑤
Bladder surface temperature
Accumulator surface temperature
Hydraulics surface temperature
Bladder conditional temperature alarm
System pressure
Bladder load changes

Static thresholds

Static thresholds are monitored by two calculated values (for details see section Calculated values).

On the one hand, the number of load changes determined via a calculated value is monitored. The threshold for this can be taken from the manufacturer’s data sheet.

On the other hand, a condition consisting of two measured values is checked using calculated values:

Bladder temperature > 30°C

AND

Temperature difference between bladder and accumulator < 2K

Only if both conditions are true, a bladder rupture is likely and an alarm will be triggered.

Dynamic thresholds (SmartLimitWatcher)

Dynamic thresholds (SmartLimitWatcher) provide information about the status of the bladder function. For this, the system pressure is monitored as a target variable. To calculate the dynamic thresholds, the following auxiliary parameters are used:

Bladder temperature
Accumulator temperature
Hydraulics temperature
Pump speed as status indicator
Vibration values of the pump

Ticket processing rules

This function can be used to easily define what should happen after a warning or alarm has been triggered, e.g.:

Email notification
SAP integration

For applications where regular refilling is necessary, it is advisable to optimise the replenishment process, for example by sending an email notification to a defined group of recipients responsible for the production supply as soon as the specified level in a tank is not reached any more, so as to trigger the refilling process.

Find out more about SFI Shop Floor Integration

Calculated values

Using calculated values, additional information can be generated from measured values.

Conditional alarm - bladder

In the following flow diagram, two measured values are compared. Only if the condition for both measured values is met 1 is output, otherwise 0 is output.

Bladder temperature
Constant as comparison value for bladder temperature
Temperature difference between bladder and accumulator
Constant as comparison value for temperature difference
Comparison ① greater than ②
Comparison ③ less than ④
AND operation between comparisons ⑤ and ⑥
Conversion of binary to numerical value
Output of result (0 = conditions not met, 1 = both conditions met)

Counting the load changes of a bladder

In the following flow diagram, the load changes of a bladder are counted. They are an indicator of bladder wear. The system pressure is monitored and compared to minimum and maximum values. If the maximum pressure is exceeded, the counter is incremented and further incrementing is blocked until the system pressure is below the minimum pressure once.