newbie: temp sensor schematic doesn't show where lm34 is placed (schematic link inside)

[jenni-18]

I'm building a temperature sensor board shown from

http://hbd.org/mtippin/thermometer.html
using the circuit "Converting a 9V DPM to a 0-2V Ground-Referenced DPM"

but I'm unsure where LM34 goes. LM34 also has 3 leads, and the article says
something about a resistor needed to be installed. Does anyone know where
these parts should go?

Thanks,
J.

 

[jenni-18]

Thanks.
I read it several times and tried my best to look for an equivalent circuit
in the application notes. Does this look right?
http://furlandia.tripod.com/temp/gnd-ref.gif

 

[CFoley1064]

Thanks.

I read it several times and tried my best to look for an equivalent circuit
in the application notes. Does this look right?
http://furlandia.tripod.com/temp/gnd-ref.gif

Yes, you've got it. The LM34 has a voltage output, and your resistor is just
functioning to provide a ground-referenced load for the LM34 output (which only
sources current, as I remember). That's also important if you've got any
distance between the sensor and the amplifier, for several reasons.

Questions of this type are better posted (and usually more enthusiastically
answered) on sci.electronics.basics.

Good luck on your project.
Chris

 

[Fred Bloggs]

Thanks.
I read it several times and tried my best to look for an equivalent circuit
in the application notes. Does this look right?
http://furlandia.tripod.com/temp/gnd-ref.gif

A basic temperature probe would look like so- if you have motors or
relays nearby then use shielded probe wiring and GND shield to Batt(-):

Please view in a fixed-width font such as Courier.




+--------------------------------------------+
| | DMM
| +----------------------+
| | PWR+ |
| | |
| +---------|IN HI - - - |
+--------+ | | | | | | | | |
| | | | -- - - - |
| | | | | | | | | | |
| 9V | | +---- |IN LO - o - - |
----- | | | | |
--- | | | | 2.00FS |
| Batt | | | | PWR- |
| | | | +----------------------+
+------+ | | | |
| | | | | |
| \ / | | |
| / \ | +------------------------------ \
| \ / +---------------------------------- \
| / \ | \ /
| \ / | / \
+----- / \ ----------------------------------+ \ /
\ / / \
/ \ \ /
\ / <----------------TWISTED PAIRs--------------> / \
/ \ \ /
\ / / \
/ \ PROBE \ /
\ / +------------------------------------+ / \
/ \ | LM34 | \ /
\ / | +-----------+ | / \
/ \ | | | 2.2k | | |
\ / +----|PWR+>-+-|+Vs Vout|-+-/\/\->IN HI +--+ |
/ \ | | | | | | | |
\ / | | | | GND | | | |
/ \ | | | +-----------+ | | |
\ / | | | | | | |
/ \ | | | +-------|------>IN LO |----+
\ / | | === | | |
/ \ --+ | 0.1u - / |
------+ | | V \ |
| | | - 18k |
| | | | 2x \ |
| | | - 1N914 / |
| | | V | |
| | | - | |
| | | | | |
+----|PWR->-+-------+-------+ |
+------------------------------------+

 

[Spehro Pefhany]

A basic temperature probe would look like so- if you have motors or
relays nearby then use shielded probe wiring and GND shield to Batt(-):

Are you not assuming they are using an external reference in the DPM?
Tying COMMON to a lower voltage than V+ - 2.8V (typical) will take the
COMMON level out of regulation wrt V+, and In LO is normally tied to
COMMON inside the DPM.

Please view in a fixed-width font such as Courier.




+--------------------------------------------+
| | DMM
| +----------------------+
| | PWR+ |
| | |
| +---------|IN HI - - - |
+--------+ | | | | | | | | |
| | | | -- - - - |
| | | | | | | | | | |
| 9V | | +---- |IN LO - o - - |
----- | | | | |
--- | | | | 2.00FS |
| Batt | | | | PWR- |
| | | | +----------------------+
+------+ | | | |
| | | | | |
| \ / | | |
| / \ | +------------------------------ \
| \ / +---------------------------------- \
| / \ | \ /
| \ / | / \
+----- / \ ----------------------------------+ \ /
\ / / \
/ \ \ /
\ / <----------------TWISTED PAIRs--------------> / \
/ \ \ /
\ / / \
/ \ PROBE \ /
\ / +------------------------------------+ / \
/ \ | LM34 | \ /
\ / | +-----------+ | / \
/ \ | | | 2.2k | | |
\ / +----|PWR+>-+-|+Vs Vout|-+-/\/\->IN HI +--+ |
/ \ | | | | | | | |
\ / | | | | GND | | | |
/ \ | | | +-----------+ | | |
\ / | | | | | | |
/ \ | | | +-------|------>IN LO |----+
\ / | | === | | |
/ \ --+ | 0.1u - / |
------+ | | V \ |
| | | - 18k |
| | | | 2x \ |
| | | - 1N914 / |
| | | V | |
| | | - | |
| | | | | |
+----|PWR->-+-------+-------+ |
+------------------------------------+

Best regards,
Spehro Pefhany

 

[Fred Bloggs]

Are you not assuming they are using an external reference in the DPM?
Tying COMMON to a lower voltage than V+ - 2.8V (typical) will take the
COMMON level out of regulation wrt V+, and In LO is normally tied to
COMMON inside the DPM.

I am assuming a basic DPM with internal converter so that the input
range will be +/-FS. Something like the DATEL DM-3100X series.

 

[Fred Bloggs]

That one uses an internal reference, and isn't representative of the
cheapie modules. COMMON is brought out as ANA. RTN.

http://www.datel.com/data/meters/dm-3100x.pdf

The LM324 schematic in the above "tripod" link shows a typical cheapie
DPM module, which obviously has COMMON tied internally to IN LO, and
is no doubt using the internal zener in the 7106 as the reference.

Okay- well in that case a 200mV unit should be used because 2V would
require the 324 Vo,max=(V+)-0.8V.

 

[Fred Bloggs]

That one uses an internal reference, and isn't representative of the
cheapie modules. COMMON is brought out as ANA. RTN.

http://www.datel.com/data/meters/dm-3100x.pdf

The LM324 schematic in the above "tripod" link shows a typical cheapie
DPM module, which obviously has COMMON tied internally to IN LO, and
is no doubt using the internal zener in the 7106 as the reference.

Among the cheapies, DigiKey carries :
http://rocky.digikey.com/WebLib/C-Ton Industries/Web Data/DK540-570 Series.pdf
at $37.90 the CDPM542-ND has 2.0V input range and 0.1%FS accuracy. This
can be adapted for battery operation like so-making a -50 TO +200 oF
thermometer:

Please view in a fixed-width font such as Courier.


FAHRENHEIT THERMOMETER
+-----+
+------------+78L05+----+--------------------+
| +--+--+ | | CDPM542
| | 1u | +----------------------+
| +---||--+ | +5V |
| | | |
| | +---------|IN HI - - - |
+--------+ | | | | | | | | | |
| | | | | -- - - - |
| | | | | | | | | | | |
| 9V | | | +---- |IN LO - o - - |
----- | | | | | |
--- | | | | | 2.00FS |
| Batt | | | | | GND |
| | | | | +----------------------+
+------+ | | | | |
| | | | | +------------------+--------------+-+
| \ / | | | | |
| / \ | | | | |
| \ / | +----------------------------------- | |
| / \ | | \ / |
| \ / +----------------------------+ / \ |
| / \ 1N914's | \ / |
+----- \ / ------------------|<|-|<|---------+ / \ |
| / \ \ / |
| \ / <----------------TWISTED PAIRs--------------> / \ |
| / \ \ / |
| \ / / \ |
| / \ PROBE \ / |
| \ / +------------------------------------+ / \ |
| / \ | LM34 | \ / |
| \ / | +-----------+ | / \ |
| / \ | | | 2.2k | | | |
| \ / +----|PWR+>-+-|+Vs Vout|-+-/\/\->IN HI +--+ | |
| / \ | | | | | | | | |
| \ / | | | | GND | | | | |
| / \ --+ | | +-----------+ | | | |
| | | === | | | | |
| | | 0.1u +-------------->IN LO |----+ |
| | | | | | |
| +----------|------+-----/\/\------+ | |
| | | 18k | |
| | | | |
+-----------------+------+------SHIELD-----------------+------+
| |
+------------------------------------+

 

[Fred Bloggs]

Among the cheapies, DigiKey carries :
http://rocky.digikey.com/WebLib/C-Ton Industries/Web Data/DK540-570 Series.pdf

at $37.90 the CDPM542-ND has 2.0V input range and 0.1%FS accuracy. This
can be adapted for battery operation like so-making a -50 TO +200 oF
thermometer:

Please view in a fixed-width font such as Courier.


FAHRENHEIT THERMOMETER
+-----+
+------------+78L05+----+--------------------+
| +--+--+ | | CDPM542
| | 1u | +----------------------+
| +---||--+ | +5V |
| | | |
| | +---------|IN HI - - - |
+--------+ | | | | | | | | | |
| | | | | -- - - - |
| | | | | | | | | | | |
| 9V | | | +---- |IN LO - o - - |
----- | | | | | |
--- | | | | | 2.00FS |
| Batt | | | | | GND |
| | | | | +----------------------+
+------+ | | | | |
| | | | | +------------------+--------------+-+
| \ / | | | | |
| / \ | | | | |
| \ / | +----------------------------------- | |
| / \ | | \ / |
| \ / +----------------------------+ / \ |
| / \ 1N914's | \ / |
+----- \ / ------------------|<|-|<|---------+ / \ |
| / \ \ / |
| \ / <----------------TWISTED PAIRs--------------> / \ |
| / \ \ / |
| \ / / \ |
| / \ PROBE \ / |
| \ / +------------------------------------+ / \ |
| / \ | LM34 | \ / |
| \ / | +-----------+ | / \ |
| / \ | | | 2.2k | | | |
| \ / +----|PWR+>-+-|+Vs Vout|-+-/\/\->IN HI +--+ | |
| / \ | | | | | | | | |
| \ / | | | | GND | | | | |
| / \ --+ | | +-----------+ | | | |
| | | === | | | | |
| | | 0.1u +-------------->IN LO |----+ |
| | | | | | |
| +----------|------+-----/\/\------+ | |
| | | 18k | |
| | | | |
+-----------------+------+------SHIELD-----------------+------+
| |
+------------------------------------+

Straightening out the shield connections:
Please view in a fixed-width font such as Courier.


FAHRENHEIT THERMOMETER
+-----+
+------------+78L05+----+--------------------+
| +--+--+ | | CDPM542
| | 1u | +----------------------+
| +---||--+ | +5V |
| | | |
| | +---------|IN HI - - - |
+--------+ | | | | | | | | | |
| | | | | -- - - - |
| | | | | | | | | | | |
| 9V | | | +---- |IN LO - o - - |
----- | | | | | |
--- | | | | | 2.00FS |
| Batt | | | | | GND |
| | | | | +----------------------+
+------+ | | | | |
| | | | | +------------------+--------------+
| \ / | | | |
| / \ | | | |
| \ / | +----------------------------------- |
| / \ | | \ / +-+
| \ / +----------------------------+ / \ | |
| / \ 1N914's | \ / |---
+--+-- \ / ------------------|<|-|<|---------+ / \ |///
| | / \ \ / |
| --- \ / <----------------TWISTED PAIRs--------------> / \ |
| /// / \ \ / |
| \ / / \ |
| / \ PROBE \ / |
| \ / +------------------------------------+ / \ |
| / \ | LM34 | \ / |
| \ / | +-----------+ | / \ |
| / \ | | | 2.2k | | | |
| \ / +----|PWR+>-+-|+Vs Vout|-+-/\/\->IN HI +--+ | |
| / \ | | | | | | | | |
| \ / | | | | GND | | | | |
| / \ --+ | | +-----------+ | | | |
| | | === | | | | |
| | | 0.1u +-------------->IN LO |----+ |
| | | | | | |
| +----------|------+-----/\/\------+ | |
| | | 18k | |
| | | | |
+-----------------+------+------SHIELD-----------------+------+
| |
+------------------------------------+

 

[James Meyer]

Straightening out the shield connections:
Please view in a fixed-width font such as Courier.


FAHRENHEIT THERMOMETER
+-----+
+------------+78L05+----+--------------------+
| +--+--+ | | CDPM542
| | 1u | +----------------------+
| +---||--+ | +5V |
| | | |
| | +---------|IN HI - - - |
+--------+ | | | | | | | | | |
| | | | | -- - - - |
| | | | | | | | | | | |
| 9V | | | +---- |IN LO - o - - |
----- | | | | | |
--- | | | | | 2.00FS |
| Batt | | | | | GND |
| | | | | +----------------------+
+------+ | | | | |
| | | | | +------------------+--------------+
| \ / | | | |
| / \ | | | |
| \ / | +----------------------------------- |
| / \ | | \ / +-+
| \ / +----------------------------+ / \ | |
| / \ 1N914's | \ / |---
+--+-- \ / ------------------|<|-|<|---------+ / \ |///
| | / \ \ / |
| --- \ / <----------------TWISTED PAIRs--------------> / \ |
| /// / \ \ / |
| \ / / \ |
| / \ PROBE \ / |
| \ / +------------------------------------+ / \ |
| / \ | LM34 | \ / |
| \ / | +-----------+ | / \ |
| / \ | | | 2.2k | | | |
| \ / +----|PWR+>-+-|+Vs Vout|-+-/\/\->IN HI +--+ | |
| / \ | | | | | | | | |
| \ / | | | | GND | | | | |
| / \ --+ | | +-----------+ | | | |
| | | === | | | | |
| | | 0.1u +-------------->IN LO |----+ |
| | | | | | |
| +----------|------+-----/\/\------+ | |
| | | 18k | |
| | | | |
+-----------------+------+------SHIELD-----------------+------+
| |
+------------------------------------+

Reposting an entire erroneous ASCII schematic just to add another
unneeded ASCII schematic for correction is seldom justified.

Jim

 

[Fred Bloggs]

Reposting an entire erroneous ASCII schematic just to add another
unneeded ASCII schematic for correction is seldom justified.

Jim

LOL

 

[Fred Bloggs]

I'm relieved to see that you caught the "tounge-in-cheek" component
of my post and didn't take umbrage.

Jim

Not at all- shown below is a circuit with GAIN and OFFSET adjustment to
calibrate the LM34 reading:
Please view in a fixed-width font such as Courier.


FAHRENHEIT THERMOMETER
+----------+
+---| LM2931-5 |--+ -50 TO +200 DEGREES
| +----------+ |
| 0.1u | 100u |
+--||-----+---||--+---------+--------------+------------------+
| | | | |
| | LM358 | GAIN ADJ | CDPM542-------+
| | UA |\ | _ | |2.00V +5V |
| +-+ +---------|+\| 20k /| | | |
| | | | >-+---/\/\-----|----+---|IN HI |
+--------+ | | +----|-/| | / | | | - - - |
| | | | | |/ | | +---/\/\--+ \ | | || || | |
| | | | | | | | 200k 475k | - - - - |
| 9V | | | +--/\/\---+ | \ | | || || | |
----- | | | | 20k | | 20k 20k | | - - - |
--- | | | \ | +-/\/\-+-/\/\--+---|IN LO |
| Batt | | | 953K | | | | | GND |
| | | | \ | | | |\ | +-------------+
+------+ | | | | | / OFF +--|-\ | |
| | | | |0.1u| | \ ADJ | >-+ |
| | | | +-||-+ | 2k<---/\/\-|+/ LM358 |
| | | | | | | \ 10k |/ UB |
| | | | \ | | | |
| | | | 18k +-------|----+--------------+-----------+
| \ / | \ | | |
| / \ | | | | |
| \ / | +------------|-------------------|--------- |
| / \ | | | \ /
| \ / +---------------|-------------------+ / \
| / \ | 1N914's | \ /
+----+ \ / -----------------+------|<|-|<|------+ / \
| | / \ \ /
--- | \ / / \
/// | / \ \ /
| \ / / \
| / \ PROBE \ /
| \ / +------------------------------------+ / \
| / \ | LM34 | \ /
| \ / | +-----------+ | / \
| / \ | | | 2.2k | | |
| \ / +----|PWR+>-+-|+Vs Vout|-+-/\/\->IN HI +--+ |
| / \ | | | | | | | |
| \ / | | | | GND | | | |
| / \ --+ | | +-----------+ | | |
| | | === | | | |
| | | 0.1u +-------------->IN LO |----+
| | | | | |
| +----------|------+-----/\/\------+ |
| | | 18k |
| | | |
+------------+------+------SHIELD-----------------+
| |
+------------------------------------+

 

[Gary Peek]

I'm building a temperature sensor board shown from

http://hbd.org/mtippin/thermometer.html
using the circuit "Converting a 9V DPM to a 0-2V Ground-Referenced DPM"

but I'm unsure where LM34 goes. LM34 also has 3 leads, and the article says
something about a resistor needed to be installed. Does anyone know where
these parts should go?

If the output of the LM34 is going to a high impedance
input it does not need a resistor, but if the input
is not high impedance it will give you a lot of trouble.

Check out the SBC-1 op amp circuit at:
http://www.industrologic.com/sbcapait.htm

The op amp input is high impedance, so, no resistor.

However the A/D input on our TC51 is not such a
high impedance so compare it to this connection:
http://www.industrologic.com/tc51apio.gif

As another poster suggested, check the data sheet,
as it explains this.

For everyone's information, check out the LM50.
Although it seems to be available only in a surface
mount package, it is a neat device. Its output's
offset voltage allows easy reading of temperatures
below 5 degrees F without a negative voltage, (but at
the expense of some accuracy.)

It also has a low impedance output so no external
components are needed at all, and it can drive even
a long length of wire.


Gary Peek mailto[email protected]
Industrologic, Inc. http://www.industrologic.com
Phone: (636) 723-4000 Fax: (636) 724-2288