Pyroelectric Detector!

[Natty]

hello friends,

I need ur help. I am using a PIR detector (IRA-E700STO SERIES MURATA)

I dont get any changes in the output voltage when an infrared body

is detected.. the output voltage ust produce a transition from either

+ve to -ve or from -ve to +ve.. I dont get that..

A PIR detector has an inbuilt FET. the pinout of the detector is the

Drain, Source and the Ground.

The detector is powered by supply connected to the drain.. and the

out put from the source is used for further analysis. I am a bit

confused.. I am not sure if something is wrong with the detector. I

wud really appreciate ur suggestions. thanx in advance.


Natty.

 

[Chris]

hello friends,

I need ur help. I am using a PIR detector (IRA-E700STO SERIES MURATA)
I dont get any changes in the output voltage when an infrared body
is detected.. the output voltage ust produce a transition from either
+ve to -ve or from -ve to +ve.. I dont get that..
A PIR detector has an inbuilt FET. the pinout of the detector is the
Drain, Source and the Ground.
The detector is powered by supply connected to the drain.. and the
out put from the source is used for further analysis. I am a bit
confused.. I am not sure if something is wrong with the detector. I
wud really appreciate ur suggestions. thanx in advance.

Natty.

Hi, Natty. First, it's Drain, Source, and Gate. But your description
of your test circuit is incomplete. Possibly you could look at the
data sheet

http://www.murata.com/catalog/k99/es0550.pdf

and then try a load resistor on the source, something like the
applications circuit in the sheet with a 5VDC Vcc (view in fixed font
or M$ Notepad):
`
` VCC
` +
` IRA-E700STO |
` |
` .----------. |
` | | |
` | D o---'
` | |
` | | Sig Out
` | |
` | S o-----------o-------o-------o
` | | | |
` | | | |
` | | .-. |
` | | | | 100K | 100pF
` | g o---. | | ---
` | | | '-' ---
` '----------' | | |
` | | |
` | | |
` === === ===
` GND GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

You could then amplify the output with an LM358 single supply op amp
and then see if you can get an output.

` 1/2 LM358
` VCC
` +
` Sig Out |\|
` >--------|+\ Out
` | >--o-----o
` .---|-/ |
` | |/| .-.
` | | | |20K
` | === | |
` | GND '-'
` | |
` '---------o
` |
` .-.
` | |1K
` | |
` '-'
` |
` ===
` GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

It's likely you'll get a useable signal out of this. You also might
want to use the other end of the LM358 as a slow comparator with a 10K
pullup at the output to give you a CMOS-compatible logic signal.

I'm also not sure what you mean by an "infrared body". Possibly you
might want to try just sensing the flame coming off a cigarette lighter
first, to see if your sensor works. The data sheet says your sensor is
selective as to response frequency, with a 5um long pass filter. If
you're using an narrow band infrared source (like an IR LED), it might
be the wrong frequency to respond.

Is any of this relevant? If not, could you describe what you're doing
with the FET output of the sensor, and what you're sensing, in somewhat
more detail?

Chris

 

[John Fields]

hello friends,

I need ur help. I am using a PIR detector (IRA-E700STO SERIES MURATA)

I dont get any changes in the output voltage when an infrared body

is detected.. the output voltage ust produce a transition from either

+ve to -ve or from -ve to +ve.. I dont get that.

---
The detector is doing just what it's supposed to do, which is to
sense a _change_ in temperature and produce an output when it senses
that change. What's happening is that when the sensor heats up it
sends out a voltage of one polarity while it's heating up, and then
when it starts cooling down it sends out a voltage of the opposite
polarity while it's cooling down. During the times its temperature
is steady, it does nothing.
---

 

[Natty]

Hello Chris and John,

thank you so much for ur suggestions. I will try to sort it out the way
u said. I think it is doing wat it has to do. Chris, I am trying to use
it as a motion detector. i.e to detect the infrared radiation from our
body. so it shud produce a pulse wen someone pass throu.. say across a
particular door. I am using a dual element PIR. I will soon get back to
you with my output. thanks again for ur reply.

Natty.

 

[John Fields]

Hi, Natty. First, it's Drain, Source, and Gate.

---
Actually, it's Drain, Source and Ground.

Note that the power supply is connected between the drain and ground
and that the output signal appears across the source and ground.
The gate of the FET is connected internally to the free end one of
the series-opposed connected pyroelectric transducers, with the free
end of the other transducer connected to ground. They're connected
in series-opposition so that, for ambient temperature changes,
they'll be inherently self temperature-compensating, while when a
differential thermal signal hits one transducer the charge generated
will be placed on the gate of the FET and converted to a voltage
before it exits the package.