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.
Later i tried a unit with 8748 part of the code in my uC section. This is with Ramp-up and Ramp-down using only two buttons. This works even now, The support below is an HRC Fuse Holder made of Phenolic or Epoxy Resin. The mV Terminations are on Top.
When you need a proportional control output, either 4-20mA or Time Proportional On-Off, This module is used. It does a slow PWM control, the cycle time for SSR or Thyristor Banks can be closer to Mains Frequency. The 4-20mA can be used to drive motors for turning valves for fuel or fluid heat control.
Schematics of Module
Board of Module
This module converts J, K Thermocouple and 4-20 mA Inputs to 0-2V Full Scale. These can be used for any voltage input too. The RTD module can be modified more easily for Voltage inputs. The control output can be On-Off or 4-20 mA/Proportional with another card. The 4-20mA I/O STC1000I is not complete.
Schematics of Modules
Board of Module
AVRTS2080A – Atmel Touch Library ATmega88
“The AVRTS2080A board is an ideal kit for evaluating the Atmel Touch Library implemented on the ATmega88. The kit comes preloaded with software for two buttons, one slider and one rotor.”
ATmega88PA – picoPower technology AVR Microcontroller. 8K Byte self-programming Flash Program Memory, 1K Byte SRAM, 512 Bytes EEPROM, 8 Channel 10-bit A/D-converter(TQFP/MLF).
- Flash (Kbytes): 8 Kbytes
- Pin Count: 32
- Max. Operating Frequency: 20 MHz
- CPU: 8-bit AVR
- Touch Channels: 12
- Max I/O Pins: 23
- Ext Interrupts: 24
This is the pcb board details of a Two Set Point Controllers for any process, shown here for temperature. For new types of transducers or input types, module card has to be designed or modified. The other cards remain the same.
The cabinet of these process controllers were made of steel for shielding, but the display card would still pickup EMI in some cases. These were more in instances where the Instrument supply was derived from the motor 3-phase supply. Instrumentation Supplies 230V AC must come from a Lighting Circuit of another supply arm, this has to come after conditioning with EMI-RFI filters and Servo Stabilizers or UPS if possible. This way the load spikes-glitches due to turn-on and turn-off of Motors and Heaters. dont act as a feedback to instruments. If line-load regulation is bad and mains voltage unstable, more problems can be expected.
This front panel shielding was done with a semi farady cage, by having a ground plane on the front of PCB, facing operator. This is just the negative of solder mask, but is the copper layer in front, no pth processing, even though it is two layer pcb. The solution worked well.
This contains the Main card with a Power Supply and Relay Control. On this card is connected the Display ICL7107 – Temperature controller.
The Thermocouple and Control Modules can be plugged into this card, these change the type of control and type of inputs. This way this can be made into any parameter controller with any type of input and output. But it is all set in production, not configurable at site.
So even if you make a 4-20mA output Flow Controller with this, the Main card and Display card remains the same. Only the Modules change. No Connectors are used, to make it vibration resistant.
The PCB Layout is here
STR910 ARM Evaluation Board – ST
A versatile system which can be used both for consumer and industrial product design. It has most of the needed interface for developing the gadget or industrial instrument in the card itself. – delabs
“The evaluation board includes the high performance STR912FAW44ARM966E-S microcontroller featuring Pre-fetch Queue and Branch cache, full speed USB2.0 compatible port, Ethernet 100/10 interface, Embedded MAC, a large Dual Bank Flash memory, a large SRAM and Embedded Trace Macrocell for development tool trace support.”
- CAN 2.0B interface
- 3 RS232, with one supporting full modem control
- Infrared Data Access (IrDA) interface
- Ethernet interface (IEEE-802.3-2002 compliant)
- USB 2.0 compliant interface with full-speed (12 Mb/s) data transmission
- Induction motor control connector
From – ST Microelectronics