delabs Circuits

Showing posts with label Process-Calibration. Show all posts
Showing posts with label Process-Calibration. Show all posts

Sunday, February 07, 2016

Millivolt Circuit ICL7129 MAX7129

My application is to calibrate some instruments with help of this source. I've studied your circuit earlier also., but I want a battery operated mV source. upto 100mV full scale which is portable but still very accurate. The better the accuracy more good for me! I want to use 9v battery or a set of rechargeable batteries for powering this circuit.

I've constructed some prototype tell me how can I send you the schematic? (file format e.g. jpg, *.tiff, *.bmp etc..., i'm using Orcad 9.2 and Express PCB Schematic softwares for Schematics).

Also I need a 4 1/2 digit LCD display for this circuit(Or any good one). I'm referring ICL7129/ Max7129 IC datasheet for this. Do you have any 2v DVM/ DPM circuits, can you please email me the same! ...please!

Mail from MO

Beckman Multimeter with the  ICL7129

"Unlike the HD110 however, this is a 20,000-count 4½ digit model with RMS-responding AC capability."

Beckman Multimeter with the  ICL7129

ICL7129A - Low-Noise, 4 1/2 Digit, Single-Chip ADC with Multiplexed LCD Drivers

The Maxim ICL7129A/MAX7129 is a high precision monolithic 4-1/2 digit A/D converter that directly drives a multiplexed liquid crystal display. Using a novel "successive integration" technique, the

About millivolt source look here Circuits FAQ - Millvolt Source see another see millivolt source, pdf at Analog-2 - Instrumentation Circuits

delabs


I have completed the millivolt circuit, but I need some more information regarding using ICL7129 for driving a 4 1/2 digit LCD for displaying the

Mail from MO

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.

delabs

Sunday, January 18, 2015

Building a mV Milli-Volt Calibrator Source

Hi, I am trying to build this mV source that you have drawn on your site. It requires a 5vdc power source with a 1k resistor in line with a 10K pot. Your schematic shows also with the pot a 10k resistor and a 100E component which I have no idea what that is.

My question to you is... does the 10K pot include the 10K resistor and the 100E component or are they separate from the pot? If they are separate, what is the 100E component?

Thanks, Ken



Dear Ken

I would like to know the Circuit File you were referring, i have many on my site for instruments.  Let us understand the Theory so you can build your own.

First - You need a Regulated Power Supply for these circuits to be accurate enough. We do not need things like 0.01% for Industrial Electronics or Field Calibration. You can always keep one of these accurate ones in your Lab.

Second - Now to bring down the Voltage of say 5V to mV, we need to Attenuate right. An attenuator contains Two Resistors. The High Value - like 1K is a Fixed MFR 1% Resistor. This faces the 5V and Then comes a Multiturn Pot, preferably Bourns or Spectrol 10 turn, This is 10K. These two form just the One part of the attenuator.

Third - This is a 50 ohm or 100 ohm shunt made of 1/2W MFR 1% or Resistors in parallel to get the value. The reason being that the shunt should not even warm up.  The 1K resistor is to protect the pot when wiper is at the 0 ohms end and the shunt is shorted by some mistake.  If all these can be built in a box with a fixed temperature using an artificial oven. AND.  If you make the Regulated Supply using Opamps and a Precision Reference. You have Laboratory grade Instrument, almost.


Hi Anantha

This is the site location that I am referring to. The 100E is confusing me.

Building a mV Milli-Volt Calibrator Source

Thanks


In this Circuit, The 100 ohms is very important as it acts like a Low Impedance Voltage Source. In Fluke Sources 50 Ohms is standard. The Voltage across this resistor is in millivolts due to the attenuation.

10K/100 ohms  is 10,000 ohms divided by 100 ohms. That gives a Divide by 100

5 Volts divided in 100 parts Gives 50 mV (approx as we have the bourns 10 turn pot before the 10K/100 ohms divider. )

See another design here  Current Source mA for calibration

This is easy to rig millivolt source for field calibration or troubleshooting of 4-20 mA current loops. Here a Darlington pair is used for current amplification which reduces the Ib error as gain is very high.

A rotary switch selects, 4-12-20 mA Preset points. A Bourns multi-turn wirewound Pot can also be used with a digital dial. Enclose in a dust proof handheld box. Read more on process calibration.
Current Source mA for calibration

You can also use one of the Arduino Analog Outputs and Attenuate them after filtering with a cap. This creates a Programmable Millivolt Source.

So, the 100E is just a 100 ohm resistor aside from the 10K pot? What does the "E" stand for?



E means Ohms. Philips used this notation first as the Symbol Ohm was difficult to Print.

100 Ohm Resistor is important, when you connect it to a Device to Calibrate it will not load it. A DMM has a 10 Meg Ohm Measurement Load. The Instrument you calibrate must have around 1 Meg or more. That is why we use FET input Opamps  to measure the mV of Thermocouples.

That is where the millivolt source steps in, it is a Thermocouple Simulator.  Read more here

OMEGA Web Technical Reference

 See the Literature at the bottom  OMEGA Web Download Literature



thank you very much Anantha
Ken

Saturday, December 13, 2014

Millivolt Source for Calibration

I was looking for a simple MILLIVOLT SOURCE for ion electrode testing and came across your pdf schematic. This design would appear to fit my needs perfectly, but I have a couple minor questions that I hope you could provide answers for:

The pdf drawing (Document Number ST02) is not clear with respect to the U4 op amp circuit, namely the connection of components R9, P4, and R10 to the op amp. I assume they connect to U4 pin 1 and pin 8 respectively as a balance or offset feature -- maybe you can confirm this.

Also, it is not shown where the terminals of the potentiometer P4 connect to -- do they go to Vcc and Vdd? And where does the slider 2 connect?

There is no problem with the rest of the circuit being readable. I expect capacitor C7 would have to be a low leakage type.

NPN transistor Q1 is shown as a BELL100, which I could not find in my catalogues. Could you suggest a suitable replacement?

Thank you for taking the time to check these points. Your answers will help in bread boarding this instrument

mail from AS


R9, P4 and R10 are for balance and offset as you said you can use it that way, but see the new circuit.

Millivolt Source for Calibration

Millivolt Source In this link see at bottom this circuit millivolt source, pdf.

I have put a better offset null, OP07 has around 75uV offset error which may show as +/- 1 count error on 4 1/2 DPM 19999 counts. You can skip it if you are using a 3 1/2 digit DPM as the error will not show, even it 4 1/2 it may be upto 2 counts only.

C7 can be a low leakage plastic cap, even a tantalum electrolytic is ok, aluminum electrolytic may cause a very small error.

Q1 can be any npn that can take 100mA current, do not use RF devices, 2N2222 is best.

If you use a DPM protect DPM inputs with clamping diodes or zeners or an error in bread-boarding may send +/- 12V to DPM and it may be damaged. Some DPMs come with protection like DMMs. use the circuit in del2003.pdf in analog section to make a 4 1/2 DPM.

Also in 2000mV range do not short outputs as the Q1 may get damaged, and in 200mV and 20mV range the output impedance is 10 ohms which is good for calibrating any high input impedance instrumentation like a process indicator etc. loading with 100K 10K will cause error.
Most instruments are very high impedance so it is fine.

delabs