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Alpha 634A

Alpha 634A Isolated Digital and Analogue I/P Processor

What is the Alpha 634A Isolated Digital and Analogue I/P Processor?

The 634A module provides six digital inputs for counting, frequency or status measurements. Counting and frequency measurements on these channels support inputs to 15KHz. The first four channels can also be configured as two quadrature phase decoder channels each with two phase inputs. Four independently isolated analogue channels are included, with input range options. Each of these analogue channels has it’s own ADC running continuously. The technique used is continuous integration, which offers the best noise performance in real world conditions by using all the available signal instead of sampling the signal at discrete intervals. The primary integration period is 3.3mS. Typically, three measurements are averaged to present 100 samples per second per channel for example. Other Integration times can be programmed enabling measurements to be made with 50 or 60Hz mains rejection. These measurements then derive from a continuous integration over one mains period offering fast update rates but high mains based noise rejection. Different integration times can be programmed for each analogue channel.
Each analogue channel is fully independently isolated from all digital inputs and other analogue channels using solid-state transformer isolation. This eliminates ground loop effects and provides protection to the equipment in the event of faults or incorrect wiring of input connections. It also makes a fault on one channel much less likely to affect other channels.
Ten additional opto-isolated channels for medium speed counting, low frequency, period, interval, RPM and digital status measurement are included. These channels support counting and frequency measurements to 1KHz. Four fused relay outputs are provided as general purpose auxiliary outputs.
Complete measurement scans of all channels are typically completed at 100 scans per second. To maintain exact measurement intervals and to allow a host computer some variability in communication times, the measurements are efficiently packed into a First In First Out (FIFO) measurement buffer within each 636 module. The 634A standard firmware supports normal use of the I/O facilities returning measurements efficiently to a host computer using a RS485 communications port.. The firmware has also been designed to be easily customised to specific application requirements.

As with other modules in the Alpha series, a local serial interface can be used to program and monitor operation locally independent of the communications on the RS485 network. This can be very convenient during installation or used later to diagnose application problems at the measurement site. Alternatively it could be used with a permanent local process display. Customised display output can be provided. All configuration settings are stored
in secure non-volatile flash memory.



• Analogue and digital measurements in compact DIN rail module

• Frequency and period measurements

• Quadrature phase decoder channel pairs

• Isolated 15/16 bit analogue channels

• Relay output auxiliary channels

• Second local diagnostic serial interface

• High speed comms 230KB (460KB)


Frequency Counter Status Channels

Number of channels: 6V

Input threshold: 3.5V

Input operating range: 3.5 - 12 V

Input count rate: 15KHZ

Isolation: Each channel is individually isolated


Phase Decoder Channels

Number of phase decoder inputs: 2 pairs (using the 4 freq channels)

Input threshold: 3.5V

Input operating range: 3.5V - 12V

Resolution: Two pairs offer discrimination of each edge resolving 4 counts per pulse pair

Input count rate: 15KHZ

Minimum pulse width/gap: 10uS

Isolation: Each channel is individually isolated.

Time base accuracy: Typically 0.02%


Analog Input Channels

Number of status channels per unit: 4

Input ranges: 0 -2 V(standard), 4-20mA(build option), 0-10V(build option)

Each channel can be specified seperately:

Isolation: Each channel is indivually isolated

Resolution: 15bits (300/sec) - 16bits (slower rates)

Programmable measurement rates: 300, 150, 100, 50-60, 10/sec for each channel individually

Base integration time – each measurement: 3.3mS

Selectable true integration times: 3mS, 10mS, 16.67-20mS, 100mS

Mains rejection – can be achieved by averaging consecutive measurements:

50HZ 6: measurements - 20mS integration time.

60Hz: 5 measurements - 16.667mS integration time.

Accuracy: 2V range+-0.02% reading +-0.02% of range at 23C

Temperature coefficient Typically 25ppm/C


Status,Counter,Low Frequency,Period Channels

Number of status channels per module: 10

Number of period measuring channels: 6 of above

Measuring functions: Status, counting, frequency period, interval, RPM

Max count rate: 100/sec each channel (4 channels)

Input threshold: 4V

Input operating range: 4- 24V

Isolation: each channel is individually isolated

Update rate – counters or status function: 1000/sec 4 channels, 100/sec 6 channels.

Period resolution: 1mS-single period

Multiple period measurements: Up to 100 periods (60 sec total)

Effective resolution: Down to 10uS


Auxillary Relay Output Channels

Number of relay outputs:  4

Relay output rating: 48V 2A Fused

Minimum output load(wetting): 12V/10mA

Isolation: One channel is an isolated contact pair. Three have common connections.


Status LED'S

Colour: Red



RS485 communications

RS232 communications

Channel 1-6,11-14 status level

Status of output channels


Module Dimensions

Dimensions: 180x120x65mm, DIN rail mounting.

Weight: 0.6Kg



2 part high quality rising cage clap screw terminal.



RS485 Communications Interface: Baud rates to 230KB supported (460KB is available for some app)

Measurement throughput of link: 10,000/sec (depends on application), 2000-4000 module type

Local RS232 Interface: Baud rates to 38K4 supported



Software: no internet access required



-20 to 60C ambient 0-90%RH


Power Requirements

12-36V DC or 24V AC

634A - Power<4W