I/O Types

The wiring of the I/O terminals varies based on the type of I/O provided on the various modules. There are many modules that present differing combinations of the same I/O types. In describing the wiring of the I/O modules, the wiring descriptions that follow are based first on I/O type to avoid duplicating the I/O wiring information described for each of the module models.

All input types and the analog outputs (voltage and current) are based on a common ground reference. The signal ground terminals used for the common/return connection from field contacts, sensors and actuators are labeled RET. The RET terminals can be shared between multiple input or output circuits as required. It is recommended that a common signal/earth ground termination rail be provided in the enclosure. The signal return wires from the many field devices should be connected to the common signal ground/earth rail.

Whether using the RET terminals for signal return connections or using the common signal ground rail, one RET terminal on each I/O module should be connected to a common signal/earth ground rail in the enclosure using a 16 AWG wire (or larger). This is intended to provide a solid ground path connection to each of the modules for fault energy dissipation. This will better handle a possible fault in field wiring to the inputs, outputs or return connections of the I/O modules. The objective is to limit possible damage to the miswired module and avoid damaging many modules on the terminal base backplane bus.

Digital inputs are used to monitor the state of switch contacts or discrete transistor outputs on the field equipment. Each Digital Input provides a pull-up resistance which attempts to pull the input circuit up to a typical voltage (V _S ) of 24 VDC. The field contacts are wired to the digital input as shown in a following diagram.

The field contacts will connect the DI input terminal to RET when they close. This pulls the 24 VDC level on the input down to near 0 V. The I/O module processor then interprets the 0 V as a closed contact.

The digital inputs can be used in pulse counter applications where the processor will count the number of times the input changes from 24 VDC to 0 V and the accumulated count is maintained as a pulse counter value for the application program.

Table: Digital Input Specifications

Supervised inputs are used to monitor the state of switch contacts with a supervision current through the field wire loop to detect various wiring or tamper faults. Supervised input is a mode option on the Universal Inputs.

There are three different types of supported supervised input connections.

• Series– Series Supervision uses a single resistor in series with the switch in the field. This type can detect tamper/trouble in the form of a short circuit across the wire pair.

• Parallel– Parallel Supervision uses a single resistor in parallel with the switch in the field. This type can detect tamper/trouble in the form of an open circuit in the field wiring loop.

• Series and Parallel– Series and Parallel Supervision uses two supervision resistors with one in series with the switch and the other in parallel (across the switch and resistor combination). This type can detect tamper/trouble conditions in the form of both an open and a shorted field wiring circuit.

  The wiring for Series Supervision, Parallel Supervision, and dual resistor Series and Parallel Supervision is shown in a following diagram.

Each input is handled as an analog voltage input with the field circuit biased with a pull-up resistance to 5 volts. This forms a voltage divider with the field switch and resistors. The Input configuration editor supports the user definition of the field resistor value between 1 KΩ and 10 KΩ and defines voltage thresholds dividing the various, possible states of the supervised input.

Table: Supervised Input Specifications

* For 2 resistor switch supervision, both resistors must have the same value +/-5%

The Universal Inputs support the selection of Voltage Input mode. When configured as voltage inputs, each of the input channels will monitor and record the DC voltage seen on the input terminal in the range of 0 to 10 VDC. Voltage inputs are wired as shown in a following diagram.

The number of monitored, voltage inputs depends on the I/O module model as discussed in the following sections.

Table: Voltage Input Specifications

Universal Inputs support the selection of Current Input mode. When configured for current inputs, the input channels switch the input circuit to provide a 47 Ω shunt resistance. The electronics will monitor and record the voltage drop seen across the shunt resistors. The current inputs are scaled across an input range of 0 to 20 mA. Current inputs are wired as shown in a following diagram.

When configured for current input, the inputs implement a current limit protection scheme for the shunt resistor from an overload. The input current is limited to 60 mA with a serial connected FET transistor. If this limit is reached for a period of 0.5 seconds, the protection transistor is turned off opening the current input circuit. After a 5 second delay, the transistor is turned on again to attempt a new measurement.

Table: Current Input Specifications

The Universal Inputs support the selection of Temperature Input mode. When configured for temperature input, the selected input channels are internally configured for the connection of a thermistor for measurement of temperature in the field environment. The input configuration editor supports the selection from many different thermistor types that vary in resistance value and response curves. See the specification list that follows.

For installation of thermistors, the Inputs selected in temperature input mode are connected as shown in a following diagram.

Table: Temperature Input Specifications

The Universal Inputs support the selection of Resistance Input mode. When configured as resistance inputs, the input channels will measure the resistance between the input and RET terminal in the range of 10 ohms to 60,000 ohms. For installation, the resistance inputs are wired as shown in a following diagram.

The number of resistance inputs monitored depends on the model of the I/O module as discussed in the following sections.

Table: Resistive Input Specifications

The RTD-DI-16 module supports the selection of RTD Input mode and also supports DI (Digital Input mode) when all the RTD inputs are not required.

RTD inputs include a precision current source for driving the RTD connection on the inputs allowing precision measurement of the voltage drop across the RTD elements in the field. The current varies with RTD type selection for more accurate temperature or resistance measurements.

The RTD inputs can be configured for four types of RTDs. The following table lists the types and the stimulus current used.

The RTD inputs can be installed in a 2-wire configuration where each of the RTD connections use a single input terminal. The IN and IN/3W each service a separate RTD. The RTD module supports 16 wired RTD inputs as shown in a following diagram.

For higher accuracy and tolerance for field wire length/resistance, the RTD inputs can be installed in a 3-wire configuration where both the IN and IN/3W input terminals along with the RET terminal are used for each RTD connection.

When using a Resistance Temperature Device other than those types listed in the previous table, the inputs can be selected for 2-wire or 3-wire resistance input. Instead of converting the input to temperature, an accurate resistance measurement is performed. That resistance can then be used within the Automation Server or AS-P application program and possibly converted to other engineering units with conversion equations and/or a look-up table.

For installation, the wiring of the 2-wire and 3-wire input schemes are shown in a following diagram.

Table: RTD Temperature Specifications

Table: RTD Resistance Specifications

Table: RTD Resistance Wiring

The Relay Form-A Outputs each deliver a SPST (single-pole single-throw) Normally-Open contact pair. The contact outputs are isolated with no internal connections. The relay ratings and internal spacing provide a line voltage output rating.

The relay form-A outputs are wired as shown in a following diagram.  

Table: Relay Output Form–A Specifications

The Relay Form-C Outputs each deliver a SPDT (single-pole double-throw) set of three contacts including C (Common), NO (Normally-Open) and NC (Normally-Closed) contacts. The contact outputs are isolated with no internal connections. The relay ratings and internal spacing provide a line voltage output rating.

The relay form-C outputs are wired as shown in a following diagram.

Table: Relay Output Form–C Specifications

The Voltage Outputs each deliver a voltage of 0 to 10 VDC level driven by a digital to analog converter by the application program. The voltage output is intended to drive the high impedance input of an analog control device in the field (such as actuator or speed controller). The output terminal is labeled as VO in the output type wiring diagram and delivers a voltage with reference to the electrical common/ground provided on the RET terminals.

The voltage outputs are wired as shown in a following diagram.

Table: Voltage Output Specifications

The Current Outputs each deliver a current of 0 to 20 mADC driven by a digital to analog converter by the application program. The current output is intended to drive the input of an analog control device in the field (such as actuator or speed controller). The output terminal is labeled as CO in the output type wiring diagram and delivers a current with reference to the electrical common/ground provided on the RET terminals.

The current outputs are wired as shown in a following diagram.  

Table: Current Output Specifications

 

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I/O Module Installation