Alpha 933 Event Recorder

€ - POA



What is the Alpha 933 Event Recorder?
The Alpha 933 event recorder is designed to accurately record events as they are detected. The module provides 18 fully isolated inputs for event measurement.

The intended application is for monitoring the sequence of events such as trips and control reaction in industrial plant so that for example cause and effect can be studied or the operation logged.

The main function of the Alpha 933 is to record changes in inputs against a real time reference. These events are buffered and available to be read into a host computer without the risk of missing subsequent events in the process.

Each Alpha 933 has an independent buffer which can be interrogated as required. Input signals are conditioned. Common problems, such as contact bounce, are handled flexibly so that multiple events are not recorded on mechanical contacts.

The resolution of event recording is 1ms and synchronization can be maintained between all 933 units in a distributed application.

Input state changes can also be counted without affecting the event recording function. The current sense or status and counter value of input channels can be returned to the host as required.

Counting or frequency measurements can be made on all inputs up to a maximum frequency of 400Hz and on 4 channels the maximum input frequency is 20Khz. Cycle period and interval measurements can be made on 4 inputs for improved resolution on low frequency signals.

The Alpha 933 has three auxiliary digital outputs and one digital input which can be used by a host as general purpose I/O or used internally by the firmware to achieve a local function.

Example uses include, synchronization to an external signal, or local indication of events or status of input signals. Specific operation can be easily programmed for custom applications.


  • Status, Counting, Frequency, Period, Interval and Plant Event Timing Functions.
  • 18 Channels per unit in compact DIN rail module.
  • 4 Channels support up to 20Khz Counting and Frequency Measurements.
  • 4 Channels support Period measurement.
  • Synchronized Timing measurements on all Input Channel State changes – 1ms
  • Integrity across all Alpha 933 modules.
  • Timing measurements synchronized with other Networked 933 Modules.
  • Timing measurements synchronized with other Networked 933 Modules.
  • Local Storage of Data and programming.
  • Second local programming and diagnostic interface.
  • High speed communications.


Specification Details

Input Channels:

Number of channels per unit: 18

Input isolation channel to channel: tested at 1500volts

Input threshold for logic 1: >4.5V

Input threshold for logic 0: <1.5V

Input operational range: 4.5-24V

Input current: 2.0mA @5V

De-bounce Options: 1-200ms (1 setting for channels 1-4 in event mode and channels 5-18 in all modes)

Frequency Measurements

Gate times: 1 sec, 10sec

Maximum input frequency: 20000 pulses/sec 1:1 on channels 1-4(independent of aggregate limit), 400 pulse/sec channels 5-18 at 1:1 mark space ratio (subject to aggregate max of 2000/sec)

Resolution (max): 0.1 cycles/sec

Accuracy: 0.05% reading +- 1Hz (1 sec/gate)

Accuracy: 0.05% reading +-0.1Hz (10 sec.gate)

Event Timing Measurements

Number of Channels: 18

Event measurement resolution: 1ms

Event registration between 933 units: 1ms using sync connection

Max input state change rate for counting and events recording: 400 cycles/sec 1:1 mark space,900 changes /sec /channel to aggregate, maximum of 4000 changes /sec 0.05% reading +/- ms

Buffer capacity for processing events: 250 per 18 channels

Note: In the event of the processed events exceeding the buffer capacity the vent recording would, freeze preserving the first 250 events encountered. One event however is defined as all input changes within the specified de bounce interval. (If several channels change within 100ms period, for example and the de-bounce interval was set for 100ms, then only one event entry would be recorded for all these channels). Aggregate limit applies to the number of input changes on all input channels in counting and frequency modes together excluding 20,000 frequency mode on channels 1-4.

Period Measurement

Number of channels: 4 (channel 5-8)

Maximum cycle period: 60 sec

Measurement resolution: 1ms to aggregate max of 4000 changes/sec

Accuracy: 0.05% reading +- 1ms

Multiple period measurements:

Number of averaged periods: 1-100 (channels 1-4)

Duration of multiple period: 60 sec max

Effective period of resolution: 10 uS to aggregate max of 4000 changes/sec

Accuracy: 0.05% reading +- 1ms

Sync Interference

In application using more than one 933 where the measurement of events captured on different units must be in agreement to 1 ms, then the units are connected using the SYNC I/O terminals on each 933 requiring synchronization.

An LED indicates successful synchronization and is illuminated continuously when lock is achieved on slave 933 units.

A second LED indicates the 933 unit is set up as SYNC master.

Power Requirement

Connector: 2 pole screw termianl

Voltage: 24V AC 12-28V DC

Current: 200mA at 12V 120 mA at 24v

Counting Measurement

Number of channels: 18

Max. count frequency: 65535

Max. count rate: 20000 pulses/sec 1:1 on channels 1-4 (independent of aggregate limit)

400 pulse/sec channels 5-18 mark/space ratio 1:1 subject to aggregate max of 2000/sec

Auxillary Channel Specification

Output switch ratings:

Outputs: 1,2 50mA @ 28VDC max, Non isolated, Suitable for driving small relays with isolated external

Output 3 Relay output: 1.0A @48V AC/DC

Auxiliary Digital Input: Contact closure to 0v External switch must be isolated.


RS465 Interface: See Manual, Baud rates to 153KB

RS232 Interface: RS232 Compatible Signals RX TX 0V 5V Signal levels, 9k6, 19k2 Baud, 8 Bits, even parity, one stop bit, 3-pole screw connector.

Status LED’s: 7

Function: Power / Fault Communication RS485 Communication RS232 Outputs 1-Dig. Input 1

Operating temperature range: -20 to 70°C

Relative humidity: <90% 0 to 40 °C

Vibration: 3g 0 to 400Hz in 3 planes.

Size: 180 x 100 x 40mm

Weight: 400g

Mounting: DIN rail Stackable

Stated accuracies are at 23°C

All specifications subject to change without notice: correct at time of publication.

Issue 4 specification relates to 1.01 firmware fit.


Alpha Server Brochure: [Brochure]

Alpha OPC Brochure: [OPC Brochure]

Alpha 933 Datasheet: [Datasheet]