Showing posts with label DMM-MultiMeter. Show all posts
Showing posts with label DMM-MultiMeter. Show all posts

Sunday, December 07, 2014

DMM or Digital Multi Meter

Digital Multi Meter - New Year Resolutions
  1. I will not drop the DMM from a height of 4 feet.
  2. I will not Test Live Powered equipment in the Ohms Mode.
  3. I shall not Measure Mains Voltage in The Current Mode.
  4. I shall get it calibrated once a year or at least once a decade.
  5. I shall not use it in High Energy Measurements.
  6. I will try my best not to give it to my best friend.
  7. I can remember Red is Positive and Black is negative.
  8. I will wear shoes and stand on a block of wood while i test.
  9. I shall not operate the rotary range switch at high speeds.
  10. I shall replace the probes-cables-connectors on wear-tear.
  11. I shall not accidentally keep the hot-iron near the DMM or leads.
  12. I shall not keep DMM on tall table and pull it with the leads.
DMM - How it Looks ... shown is from Fluke Electronics

DMM or Digital Multi Meter

How To Learn Electronics :

Theory must be studied once and referred to, again and again as you do practicals. One is by building DIY projects and then modifying them. Also Repair of equipment, troubleshooting, testing and calibrating. Then you know how components behave and real life limitations. Now design and engineer a product and test it at customer site. do a pilot production and test with more clients. Now you will learn to think based on practical applications.

"with hard work and innovation you can do it ! "  Solderman Talks 1702 AD

- Solderman Talks 1702 AD

Tutorials on Basics and Instrumentation Electronics

More About DMM

Tuesday, January 06, 2009

Thermocouple Temperature using DPM or DMM

Description -

If wires of two dissimilar metals are joined at both the ends and the junction formed at one of the ends, is heated more than the other junction, a current flows in the circuit due to Seebeck thermal emf. This effect is used in thermocouple temperature sensors.

The Peltier effect is the converse of above Seebeck effect, which means that if a current is forced through junctions of dissimilar metals, the junction will generate heat or absorb heat (cooling) depending on direction of the applied emf. This effect is used to make portable and small refrigerators.

Going to practical temperature measurement, we know that one of the junctions is the sensing or hot junction (Tmes) and the other junction is the terminating or cold junction (Tref), the voltage between terminals 'a' and 'b' is proportional to Tmes - Tref (and given in the Table 1) . The formula being Vab = alpha x (Tmes - Tref), where 'alpha' is the Seebeck coefficient of the thermocouple.

Thermocouple Junction

Table 1

MV Thermocouple
Temperature in Deg C As cold junction is not zero but is at room temperature (RT) add RT to temperature.
2.585 50
5.268 100
10.777 200 Example -

Feed 10.777 mV to the TC+ and TC- terminal if RT then is 30 Deg C reading on 2V DPM Will be 230 counts - 230mV.

16.325 300
21.846 400
27.338 500
33.096 600
Reference junction or cold junction at 0 deg C.

In the circuit, use only metal film resistors (MFR) of 1 per cent tolerance, as this is an instrumentation application. Power supply should be a stable +5V, -5V supply, for which one can use 7805 and 7905 regulators.

The inputs TC+ and TC- terminals should go to a 4-way barrier terminal block, the 2 extra terminals are used to mount TH1 Cu thermistor. This forms an isothermal block, which is good enough.

A simple way to make a TH1 Cu thermistor, is to take a 1 Meg-ohm 2W resistor as a former and wind 2 meters of 46 SWG enameled copper (Cu) wire (5.91 ohm/meter) over it. This gives a 12-ohm value. Terminate wire ends on resistor leads.

Circuit Diagram -

Thermocouple Temperature using DPM or DMM

Thermocouple Amplifier Circuit - PDF version of above, more details and easily printable.

Test and Calibration -

For calibration, you will need a DMM-DPM and a milli-volt source (as shown in the Fig.). First connect source to terminals TC+ and TC-, then set source to 0.00 mV (verify with DMM for zero). The output across +out and -out (use DMM) terminals must be mV representing the room temperature (RT). For example, if RT is 30° C (use a glass thermometer) then +out should be 30mV at 0mV input. Adjust VR1 till 30mV is read at +out terminal. This is 'zero cal'.
Millivolt Source
Now increase mV input to 21.85 (corresponding to 400° C). Now vary VR2 till +out terminal is at 430mV (temp. +RT). This is 'gain cal'. Now as VR1 and VR2 are interdependent you may have to repeat 'zero cal' and 'gain cal' a few times till you get the above values.

Properties of J thermocouple and design aspects of gain block used in the temperature measurement instrument are summarized below:

J Thermocouple Ansi Symbol 'J' -

  1. J is a thermocouple made of iron + VE and constantan -VE.
  2. Constantan is an alloy of copper and nickel.
  3. Full range of use is from -200° to +700°C
  4. Practical to use only from 0°C to 400°C.
  5. Useful in reducing and Alkaline atmosphere.
  6. Corrodes-rusts in acidic and oxidizing atmosphere
  7. Color code of wires negative-red and positive-white.
  8. J type is popular because of Low price and high mV output.
  9. J type TC used in rubber-plastic forming and general purpose use.

Design of Gain Block -

  1. Minimum input from thermocouple is very low like 1-2 mV. Hence ultra low offset (100uV opamp is required - OP07 used).
  2. Inputs may be subjected to wrong connections or high voltage. Use of R1 limits current and Zener ZD1 clamps voltage to safe level. (low leakage zener or use diode).
  3. Gain required is 400mV - 21.8mV that is approx 18 at 400° C. Gain Av = ( Rf + Ri ) / Ri here Rf is R7 and Ri = R5 + R6 + VR2 (in circuit value).

Design of TH1 cold junction compensation copper thermistor -

J Type TC output changes by 0.052mV per deg C as per Table 1. Copper has a temperature coefficient of 0.0042 ohm per ohm/deg C. eg. for a copper wire of 12 ohms, it is 12 x 0.0042 = 0.05 ohm/deg C.

For R1 of 5K current Thru TH1 =5V / 5K = 1mA. Change of voltage across TH1 with temperature is
0.05 x 1mA = 0.05mV / deg. This rate is same as J type TC hence it simulates cold junction

Anantha Narayan

Thursday, July 31, 2008

Build your own Meters and Instruments

These are basic measuring circuits you can build for your home lab.

I have documented a lab DMM i had built for my use many years ago. the circuits may have errors, build it only if you understand.

Analog Dial AVO Amps-Volts-Ohms meter

This was designed, keeping in mind, that sometimes we have few components available and we could be flat broke. Even that you could not carry your DMM somewhere, but you have to make some instrument for a quick need with what is available. If you are out of cash or feel like Robinson Crusoe, then this is a low cost measurement system. I designed it to practice on eagle, i am not sure how this circuit may work, it is not tested . But i have built, repaired and designed many DMMs. So there is a fair chance, parts of it may work :~) - Low cost Dial AVO meter

Auto ranging 4-1/2 digit digital voltmeter using ICL7135 of Intersil.


Basic Electronics
Basics of Electronics
Product Production
Work Discipline
Testing Points
Learning Electronics
Electronics Theory

Production Notes
Prototype Fabrication
Electrical Circuits

Scots Guide Electronics
Engineering - Wikibooks
Design Lab - Jim Svoboda
DC Circuits UOG
Socratic Electronics
Blobz Guide Electric Circuits

Product Design
Product Development
Constant Current Source
Good Voltage Regulators
Insulation Resistance
Digital Insulation Tester
DN Schematic PCB 04
DN Product Design 07

Hobby Circuits
VU Meter Circuits
LED brightness control
555 Incredible Chip
Process Control
liquid level measurement
Thermocouples and RTD
Design ADC Interface uC
Thermocouple Amplifier
IA Instrumentation 02
Temperature on DMM
Optical Proximity Switch
Analog Mux - Data Acquisition

Test Measurement
Instrumentation Automation
NI Test and Measurement
DMM Digital Multi Meter
Oscilloscope in T&M
IA Automation 01
Build Instruments
Tektronix T&M Equipment
Educators Corner – Agilent

Power Electronics
UPS Background
Transformer Connections
DN Power Electronics 03
DN Power Electronics 02
Half Bridge Convertor SG3525

Interfacing Microcontrollers
Embedded Process Control
80C31 8052 Microcontroller
Microprocessors and uC
Embedded Systems Design

Good Voltage Regulators
Relays and Contactors
Potentiometers Trimpots
Prototype Boards Types
Types of Capacitors
Types of Switches
Resistors How they Work
Coils Transformers SMPS
Mains Transformers Types
DN Components Selection 05

Tutor Gadgets
Count-Up Timer
Digital Logic Gates
Electronics Tutors

Teaching Instruments
Charles Proteus Steinmetz
Muntzing a Circuit Design
Teralab Electronics projects
Historical Instruments

Tables, Charts, Videos
Binary and Hex
Resistor Color Code
Ohms Law
Giga, Tera, Pico, Nano
High Resistance Materials

School - Analog Design
DN Analog Basics 06
DN Op-Amps 01
TI Semiconductors