Alpha 634A Isolated Digital and Analogue I/P Processor

€ - POA


What is the Alpha 634A Isolated Digital and Analogue I/P Processor?
The Alpha 634A module provided six digital inputs for counter, 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 integrating 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 op-to-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 customized to specific application requirements.


  • 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

Isolation: Each channel is individually isolated.

Input operating range: 3.5 – 12V

Input count rate: 15KHz

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.

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 based accuracy: Typically 0.02%

Status LED’s

Colour: Red



RS485 Communications

RS232 Communiactions

Channel 1-6.11-14 status level

Status of output channels:

Analog Output Channels

Number of status channels per unit: 4

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

Each channel can be specified separately:

Isolation: Each channel is individually isolated.

Resolution: 15bits (300/sec) – 16 bits (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 – 20 mS integration time.

60Hz: 5 Measurements – 16.667mS integration time.

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

Temperature coefficient: Typically 25ppm/°C

Module Dimensions

Dimensions: 180 x 120 x 65 mm DIN rail mounting.

Weight: 0.6Kg


2 part high quality rising cafe clap screw terminal.


Software: No internet access required.


-20 to 60°C ambient 0-90% RH

Power Requirements

12-36V DC or 24V AC

634A – Power < 4W


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

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

Local RS232 Interface: Baud rates to 38K4 supported.

Status, Counter, Low Frequency, Period Channels

Number of status channels per module: 10

Number of period measuring channels: 6 or 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


Alpha Server Brochure: [Brochure]

Alpha OPC Brochure: [OPC Brochure]

Alpha 634A Datasheet: [Datasheet]