Pveh, Inductive Transducer (Lvdt - Linear Variable Differential Transformer); Pveh, Pulse Width Modulation (Integrated); Pveh Fault Monitoring - Danfoss PVG 120 Technical Information

Technical Information
Electrical Actuation

PVEH Fault Monitoring

20
PVG 120 Proportional Valve Group
PVEH, Inductive Transducer (LVDT – Linear Variable Differential Transformer)
When the main spool is moved a voltage is induced proportional to the spool position. The use of LVDT
gives contact-free (proximity) registration of the main spool position. This means an extra-long working
life and no limitation as regards the type of hydraulic fluid used. In addition, LVDT gives a precise position
signal of high resolution.

PVEH, Pulse Width Modulation (Integrated)

Positioning of the main spool in PVEH is based on the pulse width modulation principle. As soon as the
main spool reaches the required position, modulation stops and the spool is locked in position.
A fault monitoring system is provided in all PVEA, PVEH and PVES modules.
The system is available in two versions:
•
The active fault monitoring type, which provides a warning signal, deactivates the solenoid valves
and drives the spool in neutral.
•
The passive fault monitoring type, which provides a warning signal only.
Both active and passive fault monitoring systems are triggered by three main events:
1. Input signal monitoring – The input signal voltage is continuously monitored. The permissible
range is between 15% and 85% of the supply voltage. Outside this range the section will switch into
an active error state.
2. Transducer supervision – If one of the wires to the LVDT sensor is broken or short-circuited, the
section will switch into an active error state.
3. Supervision of the closed loop – The actual position must always correspond to the demanded
position (input signal). If the actual spool position is further than the demanded spool position
(>12%, PVEA: >25%), the system detects an error and will switch into an active error state. On the
other hand, a situation where the actual position is closer to neutral than that demanded will not
cause an error state. This situation is considered "in control".When an active error state occurs, the
fault monitoring logic will be triggered.
Active fault monitoring:
•
A delay of 500 ms (PVEA: 750 ms) before anything happens.
•
The solenoid valve bridge will be disabled and all solenoid valves will be released.
•
An alarm signal is sent out through the appropriate pin connection.
•
This state is memorized and continues until the system is actively reset (by turning off the supply
voltage).
Passive fault monitoring:
•
A delay of 250 ms (PVEA: 750 ms) before anything happens.
•
The solenoid valve bridge will not be disabled but still control the main spool position.
•
An alarm signal is sent out through the appropriate pin connection.
•
This state is not memorized. When the erroneous state disappears, the alarm signal will turn to
passive again. However, the signal will always be active for a minimum of 100 ms when triggered.
To prevent the electronics from going into an undefined state, a general supervision of the power supply
and the internal clock frequency is made. This function applies to PVEH - and will not activate fault
monitoring:
1. High supply voltage – The solenoid valves are disabled when the supply voltage exceeds 36 V, and
the main spool will return/stay in neutral.
2. Low supply voltage – The solenoid valves are disabled when the supply voltage falls below 8.5 V,
and the main spool will return/stay in neutral.
520L0356 • Rev JA • Mar 2014