Modicon General Remote I/O Information

Modicon Remote I/O system specifications:

Minimum dB loss: -14.00 dB
Maximum dB loss: -35.00 dB
Tap losses: -14.00 dB down (drop) and –0.85 dB through (in to out)
Splitter loss: -6.00 dB between any two ports
Trunk splitter loss: -3.00 dB between any two ports
Inline terminator loss: -3.00 dB
Coaxial cable type: Quad-shield RG-6 or RG-11
Coaxial cable losses: RG-6: –6.00 dB per 1000 feet typical
RG-11: -2.00 dB per 1000 feet typical
Maximum trunk cable length: See maximum dB loss above- For the Trunk cable:
typically less than 1000 feet = RG-6,
greater than 1000 feet but less than 5000 feet =RG-11,
greater than 5000 feet = fiber optics
Minimum cable length: 10 feet between any two devices (rounded up from 8.29 feet actual)
Including drop cables
Maximum drop cable length: 142 feet
System impedance: 75.0 ohms
System base frequency: 1.544 MHz Bi-phase M (or S depending upon the PLC type)
Maximum number of drops: 32, but see maximum dB loss above

Testing Proceedures

During the certification of a system or network these aforementioned specifications are tested and checked utilizing several pieces of test equipment. A TDR (time domain reflectometer), which tests for gross faults such as opens and shorts based upon the 75-ohm impedance level. This device will also measure the total length of the cable as well. This is useful information should a portion of the cable system require replacement.
The LMT/R (loss measurement transmitter/receiver) is a test instrument that consists of a precise signal generator and a calibrated receiver tuned to the exact frequency of the Modicon R I/O system, which is 1.544 MHz. This combination test set measures the actual dB loss of the system.
A manual in-line attenuator is then taken to each remote drop and inserted inline with the drop cable. This device adds attenuation (dB loss) and when coupled with the measured losses from the previous test, determines if the remote device meets the manufacturer’s specification.

Modicon Remote I/O system equipment and operation:

A typical Modicon (or Gould, AEG, Schneider Automation, Square D) remote I/O system is a master-slave network. It consists of a head end, which depending upon the controller type (584, 984 or, Quantum), will be a remote I/O interface: either a J200, S908, or a CRP module. With the exception of the J200, they could be either a single cable (port) or a dual cable (ports) unit. Depending upon the system length, the quad shield trunk cable, may be an RG-6 or an RG-11. Drop cables are always RG-6. Most systems are linear in layout. That is they are set up with one main trunk. And all drops with their taps are placed upon that cable from the head end to the last drop with a 75-ohm terminator at the end of the line. As opposed to a splitter system, which has two main trunk lines with terminators at their ends, split somewhere along its length. These types of systems are problematic. They will discussed later.
As the cable leaves the head end, the first thing that it should encounter is a ground block. The ground block is used to provide a ground path for any electrical noise that may be on the cable system as well as to protect the head end, the back-plane and, the PLC from any high voltage AC which may accidentally get on the coax shield. However, if the first tap or splitter is located within 10 feet of the head end, it may be grounded as a substitute to the ground block. The next device should be a tap for a drop. However if the system is a split system this device could be a splitter. The cable coming from the head end should be connected to the input side of the tap. Electrically both the input and output ports on the tap are identical, but for troubleshooting purposes, it is beneficial to know the directional configuration of the cable. The drop port of the tap should have a drop cable attached and continue to the remote device. The remote device or I/O interface, may be one of several types of equipment depending on the type of controller and/or the type or series of I/O. The I/O can be of one type or a mixture, as Modicon has done an excellent job with backward compatibility. It may be 200 series, 500 series, 800 series or Quantum I/O. The 200 series I/O interfaces will be either a P451 or a P543. The 500 series I/O will have the same as the 200 series with the addition of a J540 module attached. The 800 series I/O could possibly have a J810, J812, J890, J892, P890 or a P892. The Quantum series I/O will have a CRA module.
The trunk cable, or main backbone, will then continue on to the next tap for the next drop. This cable will connect from the output side of the first tap to the input of the second tap and so on through to the end of the system. Located at the output side of the last tap, will be an end of line terminator. This 75-ohm terminator absorbs the energy transmitted from the head end to prevent any signal reflections. The absence of this terminator may cause a plethora of problems, ranging from no operation, intermittent or sporadic operation to one or more drops not functioning. This is due to a standing wave problem. Any reflected signals are always 180 degrees out of phase from the original signal. At select points, which can be calculated precisely, the two signals will cancel one another out. The points are at multiples, or harmonics, of the base frequency. Full wavelengths, half-wave lengths and one quarter-wave lengths are those points. At those specific points in the system, there will be zero volts of signal. One of the reasons that there is a minimum cable length specification is to mathematically avoid these data signal damaging wavelength overlaps. In a perfect world, the terminator would absorb the entire transmitted signal. Since there is some tolerance level in the terminator value, some of the signal is reflected. This signal, although usually minimal, can cause problems. It is due to these small-reflected signals, that splitter system configurations are not recommended. In a splitter configuration, there are two legs of the main trunk cable, each with a terminator at the end of line. As mentioned earlier, there will be some reflected signal from each terminator. For the system to function properly, these two reflected signals must cross paths and be absorbed within the splitter itself. Otherwise these reflected signals might interfere with the original data signal, causing communication problems. The easiest method of achieving this is to have the system balanced. When a system is in balance, the dB loss from the splitter out to each terminator is equal. In reality this also has some tolerance, within 1dB of each other is within acceptable limits. When originally laying out a design for a network, this is almost impossible to calculate due to as built cable lengths.
The two main items that must be considered when calculating the balance point are the actual trunk cable length and the number of drops on each leg. For example, if one leg has 3 drops and 500 feet of RG-11 cable, the total loss to the end from the splitter would be –3.55 dB (0.85 X 3 + 1 = 3.55). The other leg may only have 2 drops but have 1000 feet of RG-11 cable (0.85 X 2 + 2 = 3.7) resulting in a total loss to the end from the splitter. This would place the losses at each end within the allowable 1 dB limit. This would be a balanced system. Typically most systems are balanced after the installation, when communication problems arise. This can be an expensive method, as some cable or conduit may require rerouting. Another drawback to a splitter configuration is system expansion. The entire layout may require changing and rerouting if an additional drop(s) is added. Furthermore, troubleshooting these types of splitter configured systems requires intimate knowledge of the manufacturers specifications and operational rules.

Modicon device notes and tips:

AS-J200-000:
This is the remote I/O interface between a 584 PLC and the 200 series remote I/O interfaces.
The J200 plugs into the left hand, rear-most socket on the IOP board. Never plug or unplug the J200 when power is applied to the 584. Damage to the IOP board will result.
Always be sure to utilize the units with the gray colored grommets on the bottom where the F connector exits the chassis. These are the latest revision units. The J200 has the F connector shield tied to ground as the remote I/O system ground point. The output signal level on these units is 6.0 volts peak to peak.
These units are all single channel/cable devices.

AS-S901-100:
This is a remote I/O interface within a 984 chassis style controller. This interface allows the 984 to communicate with the 200 series style I/O. The exit connector is a BNC style connector. The shield of this BNC connector is jumper selectable on the board of the S901 itself to switch between a grounded and an ungrounded system. You must remove power and pull out the S901 board to access this jumper. The output signal level of this unit is 6.0 volts peak to peak. These units are all single channel/cable devices.

AS-S908-011, AS-S908-021:
This is a remote I/O interface within a 984 chassis style controller. This interface allows the 984 to communicate with the 800 series style I/O. The exit connector(s) is a BNC style connector.
The output signal level on these units is 3.0 volts peak to peak. These devices were manufactured as both single and dual channel/cable units.

AS-S908-110, AS-S908-120:
This is a remote I/O interface within a 984 rack/slot mounted style system. This interface allows the 984 to communicate with the 800 series style I/O. The exit connector(s) is an F style connector. The shield of this F connector is jumper selectable on the board of the S908 itself to switch between a grounded and an ungrounded system. You must remove power and pull out the S908 board to access this jumper. This unit also has a removable exec pack for the firmware revision and system configuration. The system configuration may be set as either a 32 drop system with 1024 maximum I/O points per drop or as a 6 drop system with 2048 maximum I/O points per drop.
The output signal level on these units is 3.0 volts peak to peak. These devices were manufactured as both single and dual channel/cable units.

140CRP93100:
This device is the remote I/O interface used solely with the Quantum series PLC family. It allows the PLC to function and communicate with the Quantum series I/O interfaces and the 800 series I/O interfaces directly. This unit mounts directly upon the Quantum rack. It may be placed in any available slot as it is addressed by the controller configuration. It is supplied with an F connector. The shield of this F connector is jumper selectable on the board of the CRP itself to switch between a grounded and an ungrounded system. You must remove power (not required but strongly recommended) and pull out the CRP board to access this jumper. The default setting is not grounded. These devices are manufactured as both single and dual channel/cable units. The output signal level on these units is 3.0 volts peak to peak.

AS-P451-622:
This device is the interface between the PLC and the locally (at the P451) attached 200 series I/O. The I/O connected to the side of the unit are the “odd” channel addresses. A maximum of 4, B240 housings are allowed here. Additionally, I/O may be connected to the port on the bottom of the unit. This I/O will be the “even” channel addresses. Again, 4 B240 housings are allowed. The P451 does not have enough power to run both the odd and even channels of I/O simultaneously with out an auxiliary power supply (P421), with one exception. The exception is the revision level of the I/O cards themselves. All discreet 200 series I/O modules end with the suffix of either 001 or 501. The 001 labeled units draw more power from the P451 than the 501 labeled units. Therefore the P451 will not support two full channels of I/O that have the 001 suffix. The P451 will communicate with either the J200 or the S901 directly via a cable and tap network. The drop address (1-32) is set via the dip-switches located behind the small door on the front of the communications pod mounted on the main unit. Using the latest revision, the switches are set using the switch matrix chart in the user manual. This unit also utilizes the gray colored grommet, around the F connector, similar to the J200, as an indicator for the latest revision. The connection to the B240 I/O housing is via a side mounted connector. These units are mechanically coupled via a “camming” in of the male portion of the B240 I/O housing. This connection is both critical and delicate. The female connector on the P451 is very easily permanently damaged by misalignment. The P451 is not capable of properly functioning with a redundant or hot standby system. These units are only single cable devices. The typical sensitivity of these units is usually greater than –48.00 to –53.00 dB.

AS-P451-681:
This device is the same as the above device (P451-622) with the exception that it allows 200 series I/O to interface and communicate with the newer controllers using the 800 series protocol. The main difference between these units is the two original boards within the communications pod are replaced with a single board (AS-J291-000). This single board performs the functions of both the original modem and control boards. The drop address is set via the dip-switches located behind the small panel located on the front of the communications pod. They are set using the binary-plus-one method. All zeros equals address 1.
They will also have the gray colored grommet around the F connector. These J291 equipped units will support redundancy or hot stand by systems. These units are only available as single cable devices.
The typical sensitivity of these units is usually –47.00 dB.

AS-P453-632:
This device is the interface between the PLC and the locally (at the P453) attached 200 series I/O.
It will communicate with either the J200 or the S901 directly via a cable and tap network. The I/O cards connected to the side of the unit are the “odd” channel addresses. A maximum of 4, B240 housings are allowed here. Additionally, I/O may be connected to the port on the bottom of the unit. This I/O will be the “even” channel addresses. Again, 4 B240 housings are allowed. The P453 has sufficient power to run both the odd and even channels of I/O simultaneously with out an auxiliary power supply (P421).
The various models of the P453 may include: models with 2 ASCII ports and I/O, models with 4 ASCII ports and no I/O, and the most common models, no ASCII and two channels of I/O. The P453 design consists of a main power unit and up to 3 boards installed in the lower section. The left most board is always a modem board. The correct modem board will have a daughter board installed near the F connector. The middle board, when so equipped, is always an ASCII board. Should this unit be equipped with 4 ASCII ports the right hand board will also be an ASCII board. The I/O board is always located to the far right side. These boards are connected to one another via two ribbon cables. One cable is a data cable and the other is a power cable. The I/O board has several other cables in addition to these two. The largest one is the power for the I/O cards. The smaller brown cable connector is for power monitoring and other internal functions. It is extremely critical to get this connector mated properly. Having the connector off by one pin will cause permanent damage to the power portion of the unit.
The channel address is set via the dip-switches or a rotary switch, depending upon the revision of the board, located behind the removable cover plate on the front of the unit. These switches are located on the right hand most board. The address switch settings may be obtained from the switch matrix chart in the user manual. The P453 may be used with redundancy or hot stand by systems, since it has the ability to “hold-up” the I/O for up to 1200 milliseconds, as compared to the default time of 300 milliseconds. This allows time for the PLC to switch from the primary unit to the stand by unit without dropping the I/O to facilitate a bump-less transfer. These units are only single cable devices. The typical sensitivity of these units is usually greater than –48.00 to –53.00 dB.

AS-P453-681:
This device is the same as the above device (P453-632) with the exception that it allows 200 series I/O to interface and communicate with the newer controllers using the 800 series protocol. The main difference between these units is the two original boards, the modem and the I/O boards within the lower portion of the device, are replaced with a single board that performs the functions of both of the original boards. The J290 board is installed in the right most slot. The same care must be exercised when installing the connectors to prevent permanent damage to the power supply. The drop address switches are located on the J290 board and are accessed via the removable front panel. They are set using the binary-plus-one method. All zeros equals address 1. If an ASCII board was present in the original unit, it may be utilized, but it must be upgraded to the latest level of firmware. These units will support a redundancy or hot stand by system. These units are available as both single port/cable and dual port/cable devices. The typical sensitivity of these units is usually –48.00 dB.

AS-J810-000, AS-J812-000:
This is the interface used to allow the 800 series I/O to communicate with the 200 series protocol controllers such as the 584 with a J200 or a S901 equipped 984.
These units are 800 series rack mounted and require a support power supply. They are equipped with a BNC connector. The switch settings for the J810 and the J812 are the most complex of any remote I/O device that Modicon has ever developed. You must have the user manual to properly set these switches. If you are replacing a defective J810 or J812, be sure to copy down the settings of the one that you are removing. There is also a key switch on the front of the unit. This is used to store or “learn” the I/O configuration of the racks’ I/O within the J810 after the switches are properly set and the unit is first powered up. These units are allowed to function with redundant or hot stand by systems.
The sensitivity of these units is typically greater than –52.00 dB.

AS-J890-001, AS-J892-001:
This device allows 800 series I/O to function and communicate with the controllers that utilize the 800 series I/O protocol such as the S908 equipped 984’s and the Quantum PLC series.
These units are 800 series rack mounted and require a support power supply. The drop address is set via dip-switches located on the back of the unit. The unit must be powered down and removed from the rack to set these switches. They are set using the binary-plus-one method. All zeros equals address 1.
The units with the suffix 001 and 002 both are equipped with BNC connectors and no internal 75-Ohm terminator. Because of this, the J890/J892 require an external in-line 75-Ohm terminator. These terminators have a signal loss of –3.00 dB. This is a point to consider when troubleshooting systems with these devices. As a basic rule, all BNC equipped remote devices require this external in-line terminator. Additionally, this external terminator increases the number of connection points, which are a common point of failure or intermittent connections. Units with the 101 and 102 suffix have F connectors and internal terminators and do not require the external terminator. These units are available in both single port/cable (001/101) and dual port/cable units (002/102). These units support redundancy and hot standby systems.
The typical sensitivity for these devices is –48.00 dB.

AS-P890-000, AS-P892-000:
This device allows 800 series I/O to function and communicate with the controllers that utilize the 800 series I/O protocol such as the S908 equipped 984’s and the Quantum PLC series.
These units are 800 series rack mounted and are equipped with an integral power supply. This power supply has less capacity than the external power supply supported models, therefore the I/O support I/O count will be less for these units. The drop address is set via dip-switches located on the back of the unit. The unit must be powered down and removed from the rack to set these switches. They are set using the binary-plus-one method. All zeros equals address 1. These units are equipped with F connectors and therefore do not require any external terminator. These units are available as single port/cable units only.
The ASCII ports utilized in the P892 units do not have the addressing flexibility afforded to the P453 with the J290 boards installed. If performing a system upgrade, this lack of flexibility may cause problems.
The typical sensitivity of these units is –45.00 dB.

140CRA93100:
This device is the remote I/O interface used solely with the Quantum series I/O. It allows the Quantum PLC to function and communicate with the Quantum series I/O interfaces directly. This unit mounts directly upon the Quantum rack and requires a support power supply. These units are supplied with F connectors. The drop address is set via a set of rotary switches on the back of the unit. To access these switches you must power down the unit (not required but strongly recommended) and remove it from the rack. There is a ones unit switch and a tens unit switch. The address is set using simple numeric addressing. These units are available in both single port/cable and dual port/cable devices. They will support redundancy and hot stand by systems. The typical sensitivity is –50.00 dB.

AS-0185-000:
This is the only tap specified to use in a Modicon remote I/O system. This tap has 3 F connectors. The in-line loss of this device is –0.85 dB. The tap or drop loss is –14.00 dB. There is absolutely no electrical difference between the “in” and the “out” ports on the tap, however it is highly recommended that the “in” port be connected to the cabling coming from the head end or PLC. This can greatly facilitate any troubleshooting efforts that may be required in the future. The tap is mounted upon an insulating block. This allows the tap to be normally floating above ground. Typically the only system ground is at the head-end where the PLC is located. However in some high electrical noise situations, the need arises to ground the system at a point nearest the noise source. In some cases this point may be the tap body. There is a small threaded hole to which a grounding or bonding strap may be connected. This will allow any noise a short direct path to ground.
On occasion, the tap is mounted in a moist or corrosive atmosphere. This may cause corrosion to build up between the F connector and the mating threads on the tap. In those instances, you should install insulating sleeves or “booties” as they are sometimes referred to. These sleeves are slipped over the threaded portion on the tap, then once the F connector is threaded down onto the tap; the sleeve prevents any contaminants from entering the threaded area. If the proper F connectors are utilized, the F connector seals the cable to F connector joint itself. The combination of the sleeve and the proper F connector greatly reduces any outside contamination from entering the connection and degrading the electrical characteristics.

AS-0186-100:
This is a splitter utilized on Modicon remote I/O systems. This device is equipped with 3 F connectors and has a loss of -6.00 dB between any two of its ports. It is commonly used as a trunk splitter. This is a misuse of this device. The proper use of this device is as a “combiner” when redundant or hot stand by (HSBY) units are utilized. The splitter (used as a combiner) allows data signals from two different sources (the HSBY PLC’s) to be passed between one another for system checking and should one system fail, allow the data signal to be passed through to the I/O seamlessly. When misused as a trunk splitter, the insertion losses are double what the correct device allows.

MA-0331-000:
This is a trunk splitter used on Modicon remote I/O systems. This device is equipped with 3 F connectors and has a loss of –3.00 dB between any two ports. This device can not be used as a signal combiner on a redundant or hot stand by system (HSBY). It is used to equally divide the data signal from one source into two equal parts.