GE VMIVME-3125 Analog Input Board

GE VMIVME-3125 Analog Input Board

Product Overview

VMIVME-3125 is a flexible and low-cost analog input board that adopts the VMEbus 6U single height format and provides 16 differential or 32 single ended analog input channels. The channels are digitized using a 12 bit resolution analog-to-digital converter (ADC). This board does not require software settings, and will automatically start scanning all input channels after power on or system reset. The converted data is stored in dual port memory and can be accessed immediately through VMEbus. It also has a built-in self-test (BIT) function, and the input voltage range and gain can be programmed by the user through jumper wires. The VMEbus base address and access mode can be fully selected.

Core Features

16 differential or 32 single ended analog input channels.

1 12 bit A/D converter with built-in tracking and holding function.

All inputs are automatically scanned at a total rate of 40 kHz.

Scanning can begin without software initialization.

The input range is from ± 50 mV to ± 10 VDC.

Input overvoltage protection, analog input is low-pass filtered at 50 kHz, and an optional 40 Hz low-pass filter sub board can be added.

Supports discrete or large-scale terminated cables.

Input pull-down resistor to prevent input floating.

Supports both online and offline built-in testing (BIT).

The programmable gain of the jumper is x1, x10, x100.

The optional A/D range is ± 5 VDC, ± 10 VDC, and 0 to 10 VDC.

Data access methods: D16, D08 (EO), D08 (O).

Front panel LED indicator light.

1000 VDC isolation between analog ground and digital ground.

Optional 0-20, 4-20, and 5-25 mA current input ranges.

Working principle

Functional components: mainly including VMEbus interface, analog-to-digital converter (ADC) and control logic, analog input multiplexing, gain and conversion, BIT voltage reference and multiplexer, board ID register and other functional parts.

VMEbus interface: Communication registers are mapped to 64 16 bit words (128 bytes) in memory, which can be located on any 128 byte boundary within the VMEbus short I/O space and can be configured to respond to short monitoring or short non privileged data access.

Analog to digital conversion control and timing: There are two operating modes, namely continuous scanning of all 16 or 32 analog input channels, and stopping scanning and locking to a single channel. Using a 12 bit ADC with a conversion time of 8.5 μ sec, the channel acquisition cycle is once every 25 μ sec, and the total scanning rate is 40 kHz. The ADC's built-in tracking and holding device can prevent erroneous readings from signals that change during the conversion cycle.

Built in Test Reference: Equipped with programmable precision voltage reference for board built-in testing (BIT). When selected, the BIT voltage is fed to the ADC through a programmable gain amplifier, bypassing the external analog input on channel 0. Users can enable BIT during initial board installation or real-time system self diagnosis.

Analog Input: The front panel connector provides 16 differential or 32 single ended analog inputs. It is recommended to use differential mode to reduce noise and improve common mode rejection ratio. Unused inputs should be grounded, and the low end of the differential input on the board has an internal 22 M Ω pull-down resistor.

Low pass filter: Provides a passive single pole low-pass input filter with a normal -3 dB cut-off frequency of 50 kHz, and can also be configured with an additional sub board to provide a low-pass filter with a cut-off frequency of 40 Hz.

Input multiplexer: There are two levels of analog multiplexing, with each of the 32 inputs selected through one of the four 8x1 first level analog input multiplexers. The second level multiplexer is configured as a 4x2 board, and one or two of the first level output signals are selected to provide single ended or differential operation mode. BIT reference voltage can also be selected.

Programmable gain instrumentation amplifier: After selecting the input channel and passing through the input multiplexer, it enters the programmable gain amplifier as a differential input. The differential amplifier suppresses common mode noise and delivers the scaled single ended output to the ADC. The hardware can jumper the gain to 1, 10, and 100.

Channel sequencer and dual port RAM memory: typically run in scan mode, starting conversion immediately after power on or reset. After A/D conversion is completed, the dual port control logic retrieves the conversion data and stores it in the corresponding dual port register of the channel. The channel counter increments and selects the next channel to be multiplexed to the ADC. After all input channels are converted and stored, the channel counter resets and starts the channel scanning sequence again. The channel sequencer can be stopped at the current address by the stop auto scan bit in the control/status register.

Board ID Register: The first position of the VMIVME-3125 register group is the read-only board ID register, with a value of $37, used for general system software to automatically determine the installed board.

Built in power converter and ADC power supply: The power supply for the analog circuit is provided by an onboard DC-DC converter, which converts the+5 VDC of VMEbus to a regulated ± 15 VDC. The+5 VDC logic power supply for the ADC is provided by an onboard regulator, and a separate+5 V DC-DC converter is used to provide isolated analog ground for the ADC.

Configuration and Installation

Unpacking procedure: Components may be sensitive to electrostatic discharge. When handling, the board should be placed on conductive material. After unpacking, check for any transportation damage. If there is any damage, file a claim with the carrier and report to GE.

Physical installation: Power off installation, insert the board into the appropriate slot of the chassis, ensure correct alignment and orientation, smoothly slide towards the mating connector until firmly seated.

Jumper installation

Board address: occupies a short I/O address space of 128 consecutive bytes, with the base address controlled by jumper E6 to E14. The installed jumper corresponds to binary 0, and the uninstalled one corresponds to binary 1. The factory default address is short I/O $0000 (all jumper installations).

Address modifier: Jumper E16 determines the access mode of the response, including monitoring, non privileged, or both.

Input configuration: Three jumpers (J4, J5, and E5) are used to configure single ended or differential inputs, two jumpers (E1 and E2) control the input voltage range, two jumpers (E3 and E4) control the gain, and there are filter related jumpers. The factory default configuration is single ended, ± 10 V range, and unity gain.

Analog input connector description: 16 differential or 32 single ended analog input connections are made through the front panel 37 pin D-type connector P3, with corresponding pins and signal allocation.

Calibration Procedure: To obtain the specified accuracy of analog measurements, calibration is required for the required range and input topology. Firstly, instrument amplifier offset and BIT voltage calibration are performed, and then the corresponding offset and gain calibration procedures for the input topology are selected. Calibration requires a 5-digit digital voltmeter (DVM) and precision voltage reference equipment.

Programming

Memory mapping: occupying 128 bytes of address space, including four information and control registers, as well as a conversion data register. Depending on the jumper configuration of the board (single ended or differential input, normal or maximum buffer for differential input), there are different memory mapping tables.

Register description

Board ID register: 8-bit read-only register, offset $00, value $37, used to uniquely identify the board.

Configuration register: 8-bit read-only register, offset $01, indicating the current configuration, including input mode and filter bandwidth information.

Control/Status Register: 8-bit read/write register with an offset of $02, allowing software to control the board and indicate its current status, including functions such as stopping automatic scanning, maximum buffer, complement, mode bit, LED off, etc.

Channel pointer register: an 8-bit read-only register with an offset of $03, typically storing the input channel number currently being sampled and converted. Under specific configurations, it can determine the most recently updated data register.

Data registers: Depending on the state of the maximum buffer location, there are 16 or 32 data registers. Starting from an offset of $40, each 12 bit conversion data containing its related channel is aligned to the right within the 16 bit data register.

Built in testing function: It can test the function by applying various internal reference voltages to channel 0 input. The host software can read the value of channel 0 and compare it with the expected value. There are corresponding BIT value tables for different ranges and gain settings.

Range and gain determination: The analog gain and range can be set by the user, but the software cannot directly read these settings. It is not recommended to determine the current settings through BIT voltage stimulation, as the board must be calibrated to a single gain and range setting.

Accessing data in byte form: Data registers should typically be accessed using a single 16 bit word transfer, or two consecutive byte transfers, but there is a risk of confusion caused by data updates, which can be avoided by pausing automatic scanning or ensuring that byte accesses are continuous and undisturbed.

Current input options: VMIVME-3125-200 and VMIVME-3125-300 offer different terminal resistances, and the ADC input voltage is related to the current range, allowing for the calculation of the current signal through a formula.