Electronic limit switch: automation of valves used in on/off applications

Limit switches by SAMSON
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Limit switches are suitable for automation of on/ off applications and issue an electric binary signal when the valve travel exceeds or falls below an adjusted limit. The signal can be used, for example, for switching control signals, issuing visual and audible alarms, or for connection to central control or alarm systems.

The installed limit contacts are either inductive, electric, pneumatic or software-based, depending on the device version.

The contacts, which can be overridden for the most part, can be used either as normally open contacts or normally closed contacts. SAMSON limit switches can contain up to three limit contacts depending on the limit switch version.

The limit switches can be attached to linear or rotary actuators or directly to pneumatic or electropneumatic positioners depending on the control valve assembly. The limit switch is linked axially over the shaft in rotary actuators or linked using a lever in linear actuators.

Attachment Type
3738 3768 3776 4740 4744 4746 4747
Direct attachment to SAMSON actuators   3271, 3277 3271, 3277 3379     3271, 3277
NAMUR    
VDI/VDE 3845    
Direct attachment to positioners           4763, 4765  

In SISs, valves are also used to shut off or open pipelines. The Type 3738 and Type 3776 Limit Switches can execute the safety function by performing the safety-related end position monitoring and emergency venting. An optionally integrated solenoid valve can be used for emergency venting. In this case, the limit switch discharges its pneumatic output to the atmosphere when the solenoid valve is de-energized, causing the mounted actuator to be vented.

The function is suitable for use in safety-instrumented systems. The Type 3738 and Type 3776 can be used up to SIL 2 (single device) and SIL 3 (redundant configuration) observing the requirements of IEC 61511 and the required hardware fault tolerance.

Safety Type
3738 3768 3776 4740 4744 4746 4747
Safety function (SIL)   •*   •*

* Applies to the proximity switches used in the inductive version as stated in manufacturer‘s declaration

Particularly processes where a potentially explosive atmospheres can form require plant components that meet special explosion protection requirements.
For the use in explosive atmospheres, we offer limit switches with intrinsic safety (Ex i), in flameproof enclosures (Ex d) and non-sparking design (Ex nA).

Type of protection Type
3738 3768 3776 4740 4744 4746 4747
Ex i    
Ex n      
Ex d          

SAMSON limit switches with communication capabilities can be integrated into process control and asset management systems. The Type 3738-50 Electronic Limit Switch supports FOUNDATION™ fieldbus and is efficiently powered by the fieldbus network. The Type 3776 Limit Switch has an optional ASInterface module with connection for wire breakage or short-circuit monitoring

Type 3738 3768 3776 4740 4744 4746 4747
Communication          

In safety-instrumented systems, it is essential that the valve responds on demand and fully opens to allow the medium to flow through it or closes to shuts off the medium flow within a certain time. To check whether the valve can move on demand, the Type 3738 Electronic Limit Switch performs a partial stroke test.

Type 3738 3768 3776 4740 4744 4746 4747
Diagnostics            

Together with valve accessories, pneumatic control valves serve as engineered solutions for special applications. SAMSON has been developing and manufacturing high-quality valves, actuators and valve accessories for over 100 years. Thanks to our experience and expertise as well as customer requirements, we have continuously developed the individual components and optimized their interaction.

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Public relations contact

Jürgen van Santen
Phone: +49 69 4009-1571
E-Mail: presse(at)samson.remove-this.de



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