Schematics of delabs

This is a modification of a mV Source that can be whipped up easily. You could use a DPM or Multimeter to read the output. The ability of this circuit to perform well depends on the quality of all the MFR resistors and the MultiTurn Pot. Use a Bourns 10T Pot.

Millivolt Source In this link see at bottom this circuit millivolt source

Good Soldered Joints, Keep all Resistors and temperature sensitive parts from Transformer and Regulators. Keep Ripple in power supplies low, no EMI tolerated. If you have problems, make a Battery Powered Unit. Shield well in case you are in a Electrically Noisy environment.

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Variable Parameters like voltage, current can be obtained by using a Digital Potentiometer. Microcontrollers or Counters operate FET CMOS Analog Switches. The switches configure resistor networks to adjust circuit performance. It could be a Speed Control of a Motor or Brightness of a Lamp. Volume controls and Tuners also can use this.

Description. - In this Circuit, digital potentiometer, connect pushbutton switches to fast and slow with one end to +7.5V, when you hold the button down the analog voltage will ramp up-down, fast or slow, this will enable you to make a digitally controlled millivolt source or power supply.

Digital Potentiometer - del50003

Here is a Millivolt Source i built for Calibration in the early days. It uses only CMOS Digital and Mixed Chips from Intersil and CD40xx Series.

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BCD Thumbwheel Switch is used to input-set data in digital form, this can be read by digital circuits, uC and uP systems and PLC-SCADA Interfaces.

Temperature Measurement and Control

In the early transition of analog to digital, before uP became acceptable, Digital systems without uP were made, it even had printers, RAM and displays. The uP systems were coming in, uC had not yet come and uP systems had to still win the confidence of the Prudent Industrial Design Engineer.

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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.

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In this circuit we tackle the error indicated in the earlier Current Source. The LM336-2.5V eliminates the tiny error of the regulated supply and resistors. Thereby increasing Precision to a higher degree.

The opamp mirrors the stable 2.5V across P3 + R13. With P3 Bourns 10 Turn Trimpot you can trim the current for calibration. Q1 BC557B having a Beta - hfe of 200 is used. But a higher gain or a FET here may reduce error further, that may be needed if you are going for 16 Bit or more resolution. Then even opamp needs to change.

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