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Alpha 934S and 934A

Alpha 934S and 934A Isolated Digital and Analogue I/P Processor

What is the Alpha 934S and 934A Isolated Digital and Analogue I/P Processor?

The 934S module provides three pairs of digital inputs for three 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 are provided for medium speed counting, low frequency, period, interval, RPM and digital status measurement are included. These channels support counting and frequency measurements to 1KHz .
The 934A also includes 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 934 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 (934A)

Second local diagnostic serial interface

High speed comms 230KB (460KB)

934S and 934A Specification Details

Phase decoder channels:

Number of phase decoder inputs: 3 pairs

Input threshold: 3.5V

Input operating range: 3.5 - 12v               

Resolution: The 2 pairs offer discrimmination 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%


Analogue Input Channel

Number of 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) – 16bits (slower rates)

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

Base integration time – each measurement: 3.3 mS

Selectable true integration times: 3.3mS, 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 23°C

Temperature coefficient: Typically <25ppm/°C


Status,Counter,Low Frequecy,Period Channels

Number of status channels per module: 10

Number of period measuring channels: 6 or above 10

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

Max count rate: 1000/sec each channel (4 channel

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 secs total)

Effective resolution: Down to 10uS

Auxillary Relay Output Channel (934A only)

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 connection


Status LED'S

Colour: Red

Function: Power, RS485 Communications, RS232 Communications, Channels 1-6, 11-14 – status level, Status of Output channels


Module Dimensions

Size: 180x120x65mm, DIN rail mounting,  0.6Kg



2 part high quality rising cage clamp with screw terminal



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

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

Local RS232 interface: Baud rates to 38K4 supported



Software: no internet access required



-20 to 60°C ambient. 0-90%RH


Power Requirements

12 - 36 V DC or 24V AC:  934A Power <4W,  934S Power <3W

Specifications subject to change without notice – correct at time of publication
Issue 1.02 DS934A01 Refers to 0.52 firmware release.