Understand data acquisition concepts
Understand volt-free contact measurement
Understand sensor fundamentals
Know the common sensors used for point and track circuit monitoring
Know how to “identify” a site
Know how to select sensors and volt-free contacts for differing point machine arrangements
Know how to “size” and select the most appropriate data loggers
Know the correct earthing arrangement for Mpec data loggers
Be able to produce of installation drawings

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title	Understanding Data Acquisition Concepts

Digital acquisition

Digital event recording allows you to determine the present state of any relay (picked or dropped) and any change in state of any relay.

Front and Back Contacts

You may monitor spare front (normally open) and spare back (normally closed) relay contacts. Where back contacts are monitored the state of the relay will be the inverse of the state of the contacts.

To account for this discrepancy Mpec data loggers allow you to configure a digital input as a front or back contact; the TX-L then automatically ensures the true state of the relay (picked or dropped) is captured.

State Changes

All digital inputs are continuously monitored for any change in state, whenever a change is detected the nature of the change is captured locally (UP to DN, or DN to UP) along with a timestamp accurate to within 10 mS.

Initial States

When an Mpec data logger boots or restarts, it will capture the “initial state” of every digital input, this way you can see the present state of all monitored digital inputs at all times, even if no change in state has taken place on a particular channel.

Initial states are clearly indicated in the historical log, and are marked “UP” or “DN”.

Analogue Acquire-on-Change

All analogue input channels are continuously logged using a process known as “Acquire-on-change”.

A sample is acquired when the measured value changes by more than a certain amount.

If there is no change, there is no sample acquired.

Consider the following waveform. The acquired samples are shown as dots.

The waveform first changes at a fairly leisurely pace, then there is a spike. Each time the input changes significantly, a sample is acquired. It can be seen that more data points are acquired around the spike.

Acquire-on-change is an excellent match for many railway applications. Where there are long periods without much change, very little data is acquired. Where there is more detail in the waveform, more points are acquired.

After the data has been acquired it is possible to go back and just “join the dots” and we have an accurate representation of the entire waveform, with the minimum amount of data logged and transmitted.

Two methods of Acquire-on-Change are supported, however the most common method is “absolute” acquire on change:

Absolute:

In absolute mode, a fresh sample is acquired each time the raw input signal changes by a fixed constant value, for example 5 mA.

E.g. If the last sample was acquired at 50 mA, the next sample will be acquired at +/- 5 mA, which is either 55 mA, or 45 mA. An absolute change of 5 mA is required to trigger the next acquisition.

The chart above shows how samples would be acquired along a straight line slope.

Absolute acquisition is a good fit where the minimum and maximum range of the input signal are well known and an even level of detail is required at all ranges.

Example Applications for Acquire on Change:

Rail Temperature Monitoring
Track Circuit Monitoring
Overhead Line Force and Displacement Monitoring
Insulation Resistance Monitoring
Power Consumption Monitoring

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Triggered Capture

In addition to Acquire-on-Change you may also capture analogue data using a method known as “Triggered Capture”.

Triggered Captures are the method of choice when you want to record intermittent railway events at maximum resolution.

A triggered capture will begin recording when a “start trigger event” is detected.

Analogue data on the selected channel(s) will then be recorded at maximum resolution until a “stop trigger event” is detected.

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A trigger event can be fired by a change in state of a digital input, or by an analogue input transitioning through a pre-determined threshold level.

Sometimes analogue data of interest can lie just outside the time-window defined by the start and end trigger events. To combat this, the data loggers will include analogue data of interest either side of the start and end trigger events in the final triggered capture waveform.

Where you are monitoring assets that may move in two directions, you may also assign a direction (Normal to Reverse or Reverse to Normal) to a triggered capture. In the event that the logger cannot determine direction, the direction will be labelled invalid.

Terms of Reference

Term	Type	Notes
Start Trigger	Trigger Event	A signal to begin the recording of capture data.
End Trigger	Trigger Event	A signal to end the recording of capture data.
Start Pre-trigger	Time (milliseconds)	The amount of extra data acquired before the start trigger.
End Pre-trigger	Time (milliseconds)	The amount of extra data acquired after the end trigger.
End Trigger Debounce	Time (milliseconds)	The end trigger condition must be continuously true for this time to terminate a capture. This prevents early termination due to short “glitches” in the data.
Capture Channel(s)	Analogue Data	The actual analogue data we wish the capture
Zero-Threshold	Absolute Analogue Level	Direction & Capture Group	Data Tag	Represents the system offset bias or noise floor. Any data below this level is removed from the capture data once the capture event has ended.
Direction	Data Tag	You may configure each capture such that it associates the data with a direction of movement, e.g Normal to Reverse, or Reverse to Normal
Capture Group	Data Tag	You may configure each capture to associate with other captures. This enables additional logic to spot illegal operations, such as switch machines moving both normal to reverse and reverse to normal simultaneously.
Timeout	Time (seconds)	A capture can not continue indefinitely. Should no end trigger occur, the capture will cease when the timeout is reached.

Example Applications:

Point Condition Monitoring
Powered Mechanical Signal Monitoring
Level Crossing Barrier Monitoring
Boom / Wig-Wag Lamp Monitoring

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title	Understand volt-free contact measurement

Digital inputs

Four digital inputs are provided as standard to monitor spare contacts of signalling relays.

These inputs are connected as follows:

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All of the terminals marked “C” are connected together internally.

This allows easy wiring to signalling relays using twisted pair cable, as specified in railway standards.

Internal resistors limit the sense current to a few milliamps at 24V.

The digital inputs are fully isolated to a minimum of 10M Ohm at 1,000V DC.

This isolation ensures that the inputs are fully separate from earth, the logger’s internal logic and the analogue inputs.

Digital inputs must never be connected into a live circuit (e.g. across a contact that is already in use by the signalling system).

They must only ever be connected to spare relay contacts.

Note

Extra care must be taken when monitoring geographical type relay interlockings, as there are internal connections within the relay sets which are not obvious just from the plugboard positions.

We recommend that full signal works testing procedures are used for geographical interlockings, not just Instrumentation Engineer.

Also the original interlocking diagrams should be updated – if overlay diagrams are used, there is a risk if other persons change the interlocking circuitry in future.

These inputs are for use with volt-free relay contacts only. Do not apply voltages to these inputs.

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title	Sensor Fundamentals

Analogue inputs

Analogue inputs are designed to accept industry standard 4-20mA sensors.

Many types of external sensor are available with a 4-20mA output, including current clamps, temperature sensors, pressure sensors and voltage transducers.

Each analogue card has four isolated channels, which are capable of powering 4-20mA current clamps. The terminals are:

24: 24V out
S: Signal input
0: 0V

The input impedance between S and 0 terminals is 200ohms.

The maximum output power of the 24V sensor power feed is 2W, or 83mA, per analogue input.

Note
CAUTION: The unit can support a maximum load of 2W per analogue channel or a total load of 10W per unit in the DC configuration. For example, if a constant load of 2W is applied to each analogue channel, a total of 5 channels can be utilized. If a constant load of 1W is applied to each analogue channel, all 10 analogue channels may be utilized.

Warning

Analogue inputs must never be connected directly to any signalling supplies or circuits.

This includes (but is not limited to) B24, B50, BX110, track circuits and signalling line circuits.

The simplest 4-20mA sensors only have two connections and take their power entirely from the loop. Others have three or four wires.

The four wire types use a separate signal and power ground to avoid interference between the power supply and measurement currents.

Example wiring to the different types is shown below:

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Most 4-20mA sensors specify the output at 4mA and at 20mA. The sensor output is considered linear between these two points This is the typical usable range of the sensor, however many sensors continue to drive outputs below 4mA and beyond 20mA when excited beyond their normal working range.

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title	Common Sensors for Point and DC Track Circuit Monitoring

Point Machine

Motor Current

LEM PCM20P/SP2

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A “uni-directional” “4-wire” current clamp. It is designed to measure “positive current” only between 0 and 20 Amps, AC or DC, however due to the 4-20mA nature, the sensor will read as low as -5 Amps at 0mA output. The split core means it is possible to install without disturbing existing wiring.

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Note that when designing and installing these sensors, “conventional current flow” must follow the arrow on the sensor enclosure. E.g. for a positive sensor output, current flow in the measured conductor flows from in the direction of the arrow.

Many electrically driven switch machines can get away with using a single LEM PCM20 sensor. The designer must ensure that all motor current carrying conductors pass through the sensor in the correct direction. This arrangement depending on the machine type and number of feeds.

In some scenarios there may be no spare relay contacts available to trigger a capture and maintain direction of movement information. In such scenarios you may employ two LEM PCM20P sensors, which each sensor capturing switch motor performance for a single direction of movement.

LEM PCM30P/SP2

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A “bi-directional” “4-wire” current clamp. It is designed to measure “positive and negative current” between -30 and +30 Amps, AC or DC, however due to the 4-20mA nature, the sensor will read as low as -45 Amps at 0mA output. The split core means it is possible to install without disturbing existing wiring.

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Note that when designing and installing these sensors, “positive conventional current flow” must follow the arrow on the sensor enclosure. E.g. for a positive sensor output, current flow in the measured conductor flows from in the direction of the arrow. When current flow in the measured conductor opposes the arrow. negative output is generated.

Many electrically driven switch machines can get away with using a single LEM PCM30 sensor to both trigger and capture switch motor performance in both normal to reverse and reverse directions. The designer must ensure that all motor current carrying conductors pass through the sensor in the correct direction. This arrangement depending on the machine type and number of feeds.

Hydraulic Pressure

The range of clamp-lock style switch machines manufactured by SPX typically feature two in-built pressure transducers installed at the manifold outlet of the “normal” and “reverse” drive hoses. One of these sensors will output signal during “normal” movement of the switch, whilst the other sensor will output a signal during the “reverse” movement of the switch. This is useful, as it means that direction information triggers may be obtained from these sensors without the need to monitor interface relays or valve feed circuits. Pressure is reported on a scale of 0 to 120 bar. Both transducers require monitoring for each switch machine.

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Note the sensor is “loop powered” only requiring two-wire operation.

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Valve / Relay Feeds

NIC-RI-361BB

Sometimes, there may be no mean obtaining direction of motion of a switch machine from motor current sensors alone

Motor always turns in the same direction, and no relays are available
LEM PCM30P sensors are unavailable, and there are no accessible relay contacts.

In such instances it is possible to use the NIC-RI361BB sensor to provide a “fake” relay input to a data logger.

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This current sensor features a volt-free-contact output that operates at 60 mA. This can be used to generate a digital trigger signal from an otherwise analogue reading. The signal could be from a relay coil, where no spare contacts are available, or from the solenoid valve feeds of hydraulic switch machine equipment. The sensor has no split core meaning, that existing wiring must be disconnected and rerouted thorough the sensor aperture.

Info

Note that the sensor still requires power to operate.

As a minimum a 24 V DC power connection is required, in addition to the volt-free contact wiring.

DC Track Circuits

Track Circuit Current

NIC-RI-361BD

The 4-20 mA range of this 4-wire sensor is 0 to +600 mA. This makes it ideal for monitoring DC track circuit current in most applications. They are typically fitted at the relay end, but some times at the feed end also. The sensor has no split core meaning, that existing wiring must be disconnected and rerouted thorough the sensor aperture.

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Note that when designing and installing these sensors, “positive conventional current flow” must follow the arrow on the sensor enclosure. E.g. for a positive sensor output, current flow in the measured conductor flows from in the direction of the arrow. When current flow in the measured conductor opposes the arrow. negative output is generated.

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title	Site Identification

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Every data logger that is to be connected to the Network Rail RADAR system must:

Follow a defined naming convention
Have a unique device ID

Logger Name

The naming convention is of the form:

Local Location Code specified by the local delivery unit, followed by an underscore, followed by a
Engineers Line Reference (ELR), followed by an underscore, followed by a
2 digit number used to identify an individual data logger if more than one data logger shares the same location.

Info
Contact the Network Rail Delivery Unit to obtain a list of preferred logger names

Device ID

Every Mpec data logger connected to the Network Rail RADAR system must be assigned a unique device ID by the Network Rail RADAR team. The number will be between 1 and 65,534. No other RADAR logger must share this number.

Info
Each Network Rail delivery unit manages a “pool” of device IDs. Contact the Network Rail Delivery Unit to obtain a list of device IDs

Note
If numbers are shared, the RADAR system is unable to map the incoming asset data to the correct asset in the RADAR server system.

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title	Typical Arrangement and Sensor Selection

Digital Event Monitoring

Straight forward. Select the volt-free-contacts you wish to monitor and connect them.

Check that polarity across the contact is correct.
You may use Front or Back contacts
You can be creative, using logic if you are short of inputs

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DC Track Circuit Monitoring

Consumes 1 x Analogue Channel per track circuit.

Straight forward. Connect 1 x Rowe Hankins 600 mA CT such that it captures the current flowing through the track relay coil.

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Point Machine Monitoring

One Motor CT - Relay Triggers

This solution consumes 1 x Analogue Channel and 2 x Digital Channels (max) per point end.

Current carrying conductors that carry full motor current in both directions of movement to pass through a PCM20 CT in the same direction. CT produces a positive direction waveform under all scenarios

Command / Calling Relays
Motor Relays
Detection Relays
Where no VFCs exist - Use “trip” output current clamps.

When monitoring multiple ends of the same point identity, VFC trigger inputs can often be shared amongst triggered captures, economising on inputs.

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Using time-of-operation Relays (Calling or motor relays that pick when the motor runs)

	N-R	R-N
Start Trigger	700 RWR DN to UP	700 NWR DN to UP
End Trigger	700 WI < 0.5 A	700 WI < 0.5 A
Capture Channel	700 WI	700 WI

Note
The Network Rail RADAR system will not accept a digital start and end trigger from the same channel. You may only use a digital channel one time in any capture. For example, the set-up below:

	This will not work - Same Digital Channel used for start and end trigger!
Start Trigger	700 RWR DN to UP
End Trigger	700 RWR UP to DN
Capture Channel	700 WI

Use of detection relays

	N-R	R-N
Start Trigger	700 NWKR UP to DN	700 RWKR UP to DN
End Trigger	700 RWKR DN to UP	700 NWKR DN to UP
Capture Channel	700 WI	700 WI

Once Motor CT - No Relay Triggers

This solution consumes 1 x Analogue Channels per point end.

Where the Normal to Reverse and Reverse to Normal motor feeds can be detected in isolation you can use a single PCM30 CT to act as motor current capture and trigger.

Current carrying conductors that carry current during normal to reverse operation are fed through the CT in one direction, whilst conductors carrying current during reverse to normal operation are fed through the CT in the opposing direction. This produces a positive waveform from the CT during normal to reverse operation, and a negative waveform from the CT during reverse to normal operation.

Triggers can be taken from the analogue data. No VFC inputs are required.

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	N-R	R-N
Start Trigger	700 WI > +5 A	700 WI < -5 A
End Trigger	700 WI < +0.5 A	700 WI > -0.5 A
Capture Channel	700 WI	700 WI

Two Motor CTs - No Relays Triggers

This solution consumes 2 x Analogue Channel per point end.

If LEM PCM30 sensors cannot be sourced, or it is not practical to route all motor current conductors through a single CT, then as a last resort, two LEM PCM20 sensors can be used to monitor a single set of points.

Info
Designers note, this solution almost doubles the cost of your point monitoring solution.

Current carrying conductors that carry current during normal to reverse operation are fed through one of the CTs, whilst conductors carrying current during reverse to normal operation are fed through the other CT. This produces a positive waveform on both CTs, however, only one CT will be active at any one time.

Triggers can be taken from the analogue data. No VFC inputs are required.

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	N-R	R-N
Start Trigger	700 RWI > +5 A	700 NWI > +5 A
End Trigger	700 RWI < +0.5 A	700 NWI < +0.5 A
Capture Channel	700 RWI	700 NWI

One Motor CT - Two Hydraulic Pressure CT

This solution consumes 3 x Analogue Channel per point end.

The cost of this solution is offset by the fact that the hydraulic sensors are incorporated into the switch machine power pack and do not incur additional expense.

In clamp-lock machines, the motor always turns in the same direction. Current carrying conductors that carry full motor current pass through a PCM20 CT in the same direction. The CT produces a positive direction waveform under all scenarios.

Two pressure transducers are connected. One transducer will only register pressure when operating in the normal to reverse direction. The other transducer will only register pressure when operating in the reverse to normal direction.

The pressure transducers can be used to act as event triggers.

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	N-R	R-N
Start Trigger	700 RWP > +5 BAR	700 NWP > +5 BAR
End Trigger	700 RWP < +5 BAR	700 NWP < +5 BAR
Capture Channel	700 WI, 700 RWP	700 WI, 700 NWP

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title	Sizing the System

Working out how many data loggers you require for a given installation is relatively simple.

Count how many analogue and digital inputs are required
Select the lowest cost data logger combination that satisfies these numbers of inputs:

SA380TX Hardware Variants

Configuration	Analogue Inputs	Digital Inputs
Base Unit (No Cards)	0	10
Base Unit + 1 Digital Card	0	18
Base Unit + 2 Digital Cards	0	26
Base Unit + 1 Analogue Cards	4	10
Base Unit + 2 Analogue Cards	8	10
Base Unit + 1 Analogue Card + 1 Digital Card	4	18

The SA380TX is more expensive than the SA380TX-L, it does however have advanced features, such as the touchscreen, battery back-up, advanced data processing options and master/slave capability.

SA380TX-L Hardware Variants

Configuration	Analogue Inputs	Digital Inputs
Base Unit (No Cards)	2	4
Base Unit + 1 Digital Card	2	12
Base Unit + 2 Digital Cards	2	20
Base Unit + 1 Analogue Cards	6	4
Base Unit + 2 Analogue Cards	10	4
Base Unit + 1 Analogue Card + 1 Digital Card	6	12

Master / Slave Devices

As stand-alone devices, each data logger will require an active SIM and GSM antenna in order to transmit data to the RADAR system. This can become troublesome for large installations installed in tight spaces.

Using a “Master / Slave” arrangement permits up to 7 SA380TX-L devices to connected over RS485.

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All data is marshalled through the master SA380TX device. Consequently all configuration, data collection and transmission, is controlled from the master SA380TX. In theory the maximum number analogue channels become 78, and digital channels becomes 166.

Note

The RS485 link can become overloaded when used for point monitoring if all the monitored point ends move concurrently. Mpec recommend the following limitations:

Electrically driven machines (Motor current only) 8 concurrent switch ends
Hydraulically driven machines (Motor current and pressure) 4 concurrent switch ends

Info

100 Ohm Resistors on RS485 lines are there to supress reflections.

These are required at each end of the link if the total link length exceeds 300m.
Fitment on shorter cable runs reduces signal to noise ratio, increasing the chance of data corruption in the presence of noise.

The specification for the resistors is 100 to 120 Ohms. 5% tolerance or better, 1/4 Watt or better.

Info

Master / Slave networking requires a modern SA380TX variant of Modstate 3 onward

Determine the Mod State of an SA380TX

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title	Power & Earthing Arrangements

SA380TX

The power supply is internally isolated from earth and the rest of the SA380TX.

Power can therefore be taken directly from the signalling 110V supply and no additional isolating transformer is required.

The earth pin of the IEC C6 socket is not connected internally. The unit must be earthed through its connection to the equipment racking.

The unit requires earthing for functional purposes (EMC ground). The unit does not require a protective earth connection in a rail environment.

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SA380TX-L

The power supply is internally isolated from earth and the rest of the SA380TX-L

Power can therefore be taken directly from the signalling 110V supply and no additional isolating transformer is required.

The earth pin of the mini-fit socket is connected internally. The unit may be earthed through its connection to the equipment racking or through the power cable.

The unit requires earthing for functional purposes (EMC ground). The unit does not require a protective earth connection in a rail environment.

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Versions Compared

Old Version 7

New Version Current

Key

Digital acquisition

Front and Back Contacts

State Changes

Initial States

Analogue Acquire-on-Change

Absolute:

Example Applications for Acquire on Change:

Triggered Capture

Digital inputs

Analogue inputs

Point Machine

Motor Current

LEM PCM20P/SP2

LEM PCM30P/SP2

Hydraulic Pressure

Valve / Relay Feeds

NIC-RI-361BB

DC Track Circuits

Track Circuit Current

NIC-RI-361BD

Logger Name

Device ID

Digital Event Monitoring

DC Track Circuit Monitoring

Point Machine Monitoring

One Motor CT - Relay Triggers

Once Motor CT - No Relay Triggers

Two Motor CTs - No Relays Triggers

One Motor CT - Two Hydraulic Pressure CT

SA380TX Hardware Variants

SA380TX-L Hardware Variants

Master / Slave Devices

SA380TX

SA380TX-L

Page Comparison

Versions Compared

Old Version 7

New Version Current

Key

Digital acquisition

Front and Back Contacts

State Changes

Initial States

Analogue Acquire-on-Change

Absolute:

Example Applications for Acquire on Change:

Triggered Capture

Digital inputs

Analogue inputs

Point Machine

Motor Current

LEM PCM20P/SP2

LEM PCM30P/SP2

Hydraulic Pressure

Valve / Relay Feeds

NIC-RI-361BB

DC Track Circuits

Track Circuit Current

NIC-RI-361BD

Logger Name

Device ID

Digital Event Monitoring

DC Track Circuit Monitoring

Point Machine Monitoring

One Motor CT - Relay Triggers

Once Motor CT - No Relay Triggers

Two Motor CTs - No Relays Triggers

One Motor CT - Two Hydraulic Pressure CT

SA380TX Hardware Variants

SA380TX-L Hardware Variants

Master / Slave Devices

SA380TX

SA380TX-L