Alpha 912 RTD, Resistance and Voltage Input Module

What is the Alpha 912 RTD, Resistance and Voltage Input Module?

The Alpha 912 provides 10 measurement channels at up to 19 bit resolution and 0.5uV integrity. It is fitted with general purpose dis connectable screw terminals and can be used to measure voltages, currents (using external shunts), standard Platinum RTD’s in 2,3, or 4 wire configurations and full bridge strain gauges.

The resistance mode can also be used for other resistive transducers. Strain gauge bridge offsets can be initialized.

The Alpha 912 module can be programmed to integrate signals to be measure over one or more complete mains cycle(50 – 60Hz) allowing the 912 to reject large levels of mains borne interference super imposed on micro-volt signals.

A choice of integration times and a digital filter that can be applied to any channel, together with the high stability circuitry achieve excelling noise performance and rejection.

The Alpha 912 supports an automatic range selection facility that enables maximum measurement sensitivity to be maintained for inputs that cross range thresholds.

Measurements are made continuously and can be returned in one of several formats most convenient for the supervisory software. Communications data rates up to 153KB are supported. All programming is stored in secure flash memory.

AUXILIARY INPUT/OUTPUTS

The 912 has three digital outputs and one digital input which can be used by a host as general purpose I/O or used internally by the firmware for a local function.

Example uses include, Synchronization to an external signal, or local indication of events or alarm conditions.

The standard firmware implements an alarm function that can be locally or remotely acknowledged. Specific operation can be easily programmed for custom applications.

Features

  • Voltage, Current, Resistance and Strain
  • 3 and 4 Wire RTD measurements in °C or °F
  • 13 to 19 bit resolution. 200 to 10 measurements per second.
  • Programmable Measurement Types
  • Auxiliary I/O
  • Scaling, alarm levels, filter functions.
  • Second local programming and diagnostic interface.
  • High speed communications.

Specification Details

Interference Rejction

Number of channels / module: 10

Number of poles / channel: 4

Connector type input channel: Cage clamp 2 part screw terminal

Measurement modes:

Voltage: uV DC, mV DC

Resistance: Resistance 2 terminal, Resistance 4 terminal, PT100 3 terminal, PT100 4 terminal.

Strain full bridge: 350R, 120R

AC Common mode rejection ratio channel group: <0.1uV/V

AC Single channel common mode rejection ratio: <1uV/V

DC channel common mode rejection ratio: <5uV/V

AC series mode rejection ratio 50 or 60Hz +/- 0.05%: <1mV/V (Applies to 17,18,19 bit measurements).

Maximum voltages operating:

Max. voltage between any (+) and (-) inputs: 12V

Max. voltage between any two (-) input terminals: 11V

Max. voltage between any two terminals: 22V

A-D Convertor

Overload Protection

5 Measurement resolutions are supported:

19 bits at 10 measurements/s

18 bits at 20 measurements/s

17 bits at 40 measurements/s

15 bits at 100 measurements/s

13 bits at 200 measurements/s

In addition a channel filter function can be applied to any channel. This can average the most recent four measurements.

Channel Overload Protection: Passive, 50V continuous, 150V short periods.

Voltage Measurement

Isolation

Input voltage ranges: +10V to -10V, +1.5V to -1.5V, +180mV to -180mV, +23mV to -23mV

Automatic range selection is supported.

DC Measurement accuracy: +/- 0.015% of reading +0.01% of range + 6uV

Temperature coefficients DC voltage: 25ppm rdg + 0.1uV/°C

Measurement sensitivity: <0.5uV on +23mV > -23mV range at 17bits

Note: Displayed sensitivity depends on reporting format. Additional error at 13bit 200/sec mode of 0.05% of range.

Isolation test voltage between any channel group and power supply or RS485:

Tested at 1500V at normal temperature and humidity.

Resistance Measurement

Power Requirement

Measurement Ranges: 2000 ohm, 256 ohm, 32 ohm

Sensing Current: <0.75mA(switched)

Accuracy 0.3%rdg + 0.015% rng: + 3 mohm

Accuracy (max): 1 mohm

Connector: 2-pole screw terminal

Voltage: 24V AC, 12-28V DC

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

Auxiliary Channel Specification

Output switch ratings:

Outputs 1.2: 50mA @ 28VDC max, Non isolated, Suitable for driving small relays with isolated external supply.

Outputs 3 Relay Outputs: 1.0A at 48V AC/DC

Digital Input: Contract closure to 0V, External switch must be isolated.

RTD Measurement

PT100

-50 TO 400°C +/- 0.2

-150 TO 600°C +/-0.4°C

General

RS485  Interface: See Manual, Baud rates to 153KB

RS232 Interface: RS232 Compatible Signals, RX TX 0 TO 5-volt 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 1-3

Dig. Input 1

Size: 180 x 100 x 40mm

Weight: 400g

Mounting: DIN rain Stackable

Operating temperature range: – 20 to 70°C

Relative Humidity (non-condensing): <90% 0 to 40°C

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

Programming storage: Secure flash memory Stated Accuracy’s are at 23°C

Full Strain Measurement

350 OHM Bridges:

Accuracy full bridge (repeatability): 5uE

Sensitivity at 18bits: 0.2uE (1 active gauge)

GF=2)

Energisation: 5mA pulsed.

120 OHM Bridges:

Accuracy full bridge (repeatability): 10uE

Sensitivity at 18bits: 0.6uE (1 active gauge)

GF=2) 5mA pulsed

Energisation: 5mA pulsed

All specifications subject to change without notice: correct at time of publication. Issue 3 specification relates to 1.01 firmware fit.