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Tuesday, June 16, 2015

Significance of Current Loop 4 to 20 mA Standard

Subject: delabs comments - Tell Me. message: why 4-20mA standard. why not 2-22mA or any thing else

Mail from MU

they knew you would come up with a question like this. so see this page 4-20mA Current Loop Primer and also Intrinsic Safety Circuit Design.

...transmitting 0mV or 0mA will be lost in the noise too. 4mA is enough power to go over long wires with low error due to leakages. and current ensures RFI-EMI immunity as the picked noise does not have any juice just some voltage.

4-20mA helps in Noise Immunity, Providing Power for efficient signal conditioning circuits making two wire transmitters possible.

See more at my pages Industrial Process Control Circuits

Significance of Current Loop 4 to 20 mA Standard

Hence it could be 4-20mA not mV. 0-20mA is not good enough, but is used when you just have to interface two cards or instruments close by. 4-20 mA can go from your street to the next or even much more depending on cables and voltage.


Thursday, June 11, 2015

Optical switch with photo sensors

Can you help me to find circuits which uses photo-sensors.and if you do have them, would you please send them to me.

Mail from TM

Just a few days back i have added one. It is to turn of-on water taps.

Optical Obstacle Switch. - one more here  thru all links in great detail.

Here is an image of a low cost gizmo that applies the photo-sensors to detect motion. They are called motion detectors.

Optical switch with photo sensors

How Infrared motion detector components work - Infrared radiation exists in the electromagnetic spectrum at a wavelength that is longer than visible light. It cannot be seen but it can be detected.

K30 PIR Movement Detector -  This circuit is designed around a custom motion-detection IC KC778B. The circuit utilizes both a PIR (Passive InfraRed) detector and a light-dependent resistor (LDR) to detect motion up to 6 meters away.

PIR Controller – KC778B

The MPCC has been designed for easy implementation of AC control functions that use a Passive Infra-Red (PIR) motion detector. Due to its high sensitivity and reliability, it is also widely used in security product.

PIR Controller -KC778B - Auto Camp Light

Above is an example of  camp light using the KC778B. Uses battery 12VDC. Internal voltage regulator is used,  but can work down to 7V.


Another related Question

I am working on a project where I am trying to adjust the brightness of a set of LEDs based on the amount of IR light detected.  I have experimented with using a photo transistor, but i can't seem to amplify the difference experienced enough to visibly change the brightness of attached leds.

Lighting and Power control Automation

i am researching for a project for industrial automation . in this i am having one concept that is following below

if any one of person is in room the electrical power should be connected in this time one or more persons are entering in side that room at that time also that power should be ON .Now that persons who are all inside that room one by one is coming out that power should not be OFF but the last person who is coming out side off the room that power should be OFF

this is my concept of my project for this concept please design a circuit for me please send me replay for this concept

Mail from TM

You have to count people with optical switches or infrared detectors. Then using dsp or up processors and figure how best to establish number of people in room.

See below Motion Detectors - Professional and a DIY Version

Motion Detectors - Professional and a DIY Version

See a Related circuit here Optical Obstacle Switch.

A pair of optical switch-sets for every door that leads to room. Only if object cuts both beams then you count one. It is the idea you have to develop, Circuits are on the web.

See also - InfraRed Detector for Proximity Switch and InfraRed LED Flasher for Optical Switch

A pair of optical switch-sets for every door that leads to room. Only  if  object cuts  both  beams   then you  count  one. Even windows need sensors, if you expect some to use that for movement.  But some may slip in between beams, you might  have  see that happen.

Motion detector - Wiki

An electronic motion detector contains an optical, microwave, or acoustic sensor, and in many cases a transmitter for illumination. However, a passive sensor only senses a signal emitted by the moving object itself.

Other methods are RFID fixed on every person. Then it may be foolproof. Also as  most have cellphones, track the phones with GPS and count people in room.  A footrug with a weight measurement can also count people moving thru door. But a few may jump over them, so it has to be foolproof log footrug.

Updated - 10th Jun 2015