CTI 2557-A 16-Channel RTD Input Module

The Model 2557-A is designed to translate 10 Ohm copper, 100 Ohm

platinum and, 120 Ohm nickel RTDs or millivolt input signals into

scaled digital words which are then sent to the programmable

controller (PLC).

The 2557-A RTD Input Module features built-in independent two,

three, or four lead compensation for each RTD input.

The 2557-A uses 8 8 point removable wiring connectors.

The connectors are provided with the module. Support for other

RTD types is available through special request from the factory.

Call CTI at 1-800-537-8398 to determine if support is available for

your special RTD type.

Features

• Replaces Siemens® 505-2557. CTI 2557

• 16 bit ADC for each channel

• Supports 10Ω copper, 100Ω platinum, and 120Ω nickel RTDs, and

millivolt inputs

• Advanced preprocessing with on-board scaling

• Alarm detection

• Filtering and averaging

• Fast 20 mSec update time

• Open RTD detection and lead resistance compensation

• Support for 2. 3. or 4 wire RTD elements

• Removeable connectors

Asynchronous Operation

The module operates asynchronously with respect to the PLC; a scan

of the PLC and input sampling of the module do not occur at the same

time. Instead, the module will translate all inputs in one module update

(20 milliseconds maximum) and store the translated words in a buffer

memory. The PLC retrieves the stored words from the module buffer

memory at the start of the I/O scan.

Compatibility with Immediate I/O

The Model 2557-A has been tested and is compatible with the

Immediate read function of the SIMATIC® 545 and 555 PLC.

100 Ohm, 10 Ohm, 120 Ohm RTDs, or Millivolt Inputs

Each of the module's 16 channels may be configured to receive either

a 100 Ohm platinum RTD or a 120 Ohm nickel RTD or a 10 Ohm

copper RTD input signal (two, three or four wire) or a DC voltage signal

ranging from 0 to 100 millivolts. Selection of 10 Ohm, 100 Ohm or 120

Ohm RTDs or millivolts are made via internal switch and jumper settings.

Digital Word Map

RTD and/or millivolt signals are translated into a 14-bit digital word.

Since the PLC requires a 16-bit input word, the 14-bit value from the

converter is placed into a 16-bit word for transmittal to the PLC.

As shown in the following figure, of the two bits not used for the digital

word, one is used to show the sign of the word, while the other is used

to note values which are "overrange or underrange."