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Electronic Speed Switches.. 

Electronic Speed Switch :-

 

ESS Product Catalog 

APPLICABLE STANDARDS

 

Following International and Indian standards are used for design, manufacturing and testing of Electronic Speed Switches.

      IEC-947-1 : 1988 (IS-13947 : 1993)

Standard for Low Voltage switchgears

    UL-508

Standard for Industrial Control Products

v     IS-5 : 1994

Standard for paint shades / enamels.

 CONSTRUCTION

 These models consist of two parts namely the Monitoring Unit and the Sensor Probe.

 Monitoring Unit : These are available in variety of enclosures suitable for projection / panel / wall mounting enclosures with protection grades of IP-30 and IP-65.

 Sensor Probe : These are available with different operating principles like Inductive, Magnetic or Photoelectric (Optical). Standard models are offered with Inductive Sensor probes of usually M30 size in tubular enclosure. User has to select appropriate sensor depending upon application requirements. Please refer our Catalogue of Proximity Switches and Selection Guidelines for proximity switches.

Robust protective Cast Aluminium enclosures are used for sensor probes for such specific applications where the probe is likely to be exposed to severe environmental conditions.

 
PRINCIPLE OF OPERATION

 The speed / motion of the rotating / moving object is sensed by a non-contact Inductive / Optical / Magnetic type sensor. The sensor is installed in such a way that the sensor face is in the vicinity of the object. Flag disc with specified no. of objects per revolution is mounted on the rotating object. When these flags pass across the probe sensing zone, a square wave pulse is generated by the electronic circuit in side the probe. These pulses are fed to the monitoring unit through an interconnecting cable. The interconnecting cable can extend upto 50 meters maximum without any signal amplifier.  

 These pulses are digital in nature and the circuit is designed to work in an electrically noisy environment. However, the interconnecting cable should be minimum 0.5 mm in size. An LED provided on the rear side of the probe gives visual indication whenever a flag is sensed.

The Monitoring Units are available in different circuits as per the requirements. Standard units consist of proprietary HYBRID circuit incorporating digital IC’s. The speed dependent pulses generated by the sensor probe are compared with a reference frequency generator and an effective output signal is produced to switch an output relay at the preset value.

 EXPLANATION OF TECHNICAL TERMS

 Relay Logic

Different types of relay operation logics are generally practiced. For monitoring under-speed, it is recommended to have relay energized at healthy state and trip in case the speed drops below the set value. However, different operational logic is provided for application specific requirement.

 Initial By-pass Time Delay (ITD)

The output relay of basic model operates as per the instantaneous speed value. The relay is initially in OFF state and becomes ON when the equipment speed exceeds the set value. Since the initial speed of the equipment is most likely less than the set value, an external by-pass timer contact has to be used in order to ensure build-up of the speed. Once the speed reaches above set value, the speed monitor starts its function. We provide a built-in Initial Time Delay in order to avoid the use of an external timer. This way the user can avoid the excess wiring involved in connecting external device. With this circuit, the output relay energizes at supply ON instant and remains ONN for preset time duration. This duration is adjustable usually from 1 to 20 seconds.

 Nuisance Tripping Time Delay (NTD)

While the rotating or moving machine is running at healthy speed, there are instances when the running speed drops below set value but for a very short duration and gets back to healthy state. This kind of frequent occurance is termed as fleeting fault. In order to avoid machine  tripping due to such instances, nuisance tripping delay is incorporated in our circuit. With this feature, the machine fault has to be of duration greater than the set nuisance delay. If the fault lasts for the set nuisance delay, the output relay trips. This delay is usually adjustable between 1 to 20 seconds.

 Hysterisis

The output relay has an inherent operating hysterisis characteristic as shown in fig.1. Hysterisis is the differential between relay ON and relay OFF speed values at a particular set point. Standard models are provided with about 5% hysterisis value. However, this can be preset at any other desired value if required.

 Number of Flags

These speed monitors take square wave signal from non-contact sensors. The sensor scans speed of the rotating machine by sensing objects fixed on the rotating or moving machine. There are certain number of objects crossing the sensor field per revolution. This number is referred to as Number of flags and is expressed in terms of Pulses Per Revolution (PPR). This concept is applicable for rotating machines only. For monitoring linear speed, feedback from two sensors is taken and the time difference between the two is calibrated in terms of speed in either km/hr or m/s. 

 Response Time

For rotating machines, the speed in RPM and the rotation frequency in Hz are related through following relation

 

                           (Speed in RPM) x (Number of flags)

Frequency (Hz) = -----------------------------------------

                                                 60

 

Response time is then defied as the time taken for relay to trip after detection of fault. The fault in this case means the reduction in speed below set value. This time is the reciprocal of frequency.

                                                     60

Response Time (Tr) = ----------------------------------------

                                (Speed in RPM) x (Number of flags)

 From above relation, it is clear that for a fixed speed drive, the response time is inversely proportional to Number of flags. Greater is the number of flags, lesser is the response time. Hence it is upon the user to select number of flags depending upon the criticality of response time to the application.

 However, we do recommend number of flags for certain speed ranges as given below;

 

 

Operating Range RPM

 

 

1 to 10

 

5 to 50 &

10 to 100

 

50 to 500 &

100 to 1000

 

500 to 5000

 

No. of flags

 

 

8

 

4

 

 

2

 

1

  STANDARD SPECIFICATIONS

 

v     Power Consumption : 5 VA max.

 

v     Working Temperature : 0°C to 55°C

 

v     Repeat Accuracy : Better than 0.1% of the set value.

 

v     Setting Accuracy : Analog models ±5% Digital models ±1%

 

v     Contact Rating : 5 A resistive at 250 V AC. For higher ratings contact us.

 

v     Speed Range : Standard models upto 6000 RPM

 

v     Special models for monitoring speed upto 20000 RPM are available.

 

 

      

 

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