The VTi21 can be used to monitor the in-band electrical current amplitude of the following reed track circuit frequencies
- 363 Hz
- 369 Hz
- 370 Hz
- 372 Hz
- 375 Hz
- 378 Hz
- 381 Hz
- 384 Hz
- 408Hz
- 417Hz
- 423Hz

The VTi21 implements 11 very narrow-band filters, to determine the amplitude of the current at these frequencies, with a 2.5 Hz bandwidth.
The effect is an output signal that is illustrative of the the occupancy state of the track circuit. All out-of band noise is rejected. Any deviation in frequency or level in the received signal will result in a drop in the output amplitude.
The system may be fitted on both transmitter and receiver. As both systems exhibit the same current range.
The output rate of the system is 3 samples per second.

0802 Reed Track Circuit

Operates at 369 Hz
Red Trace is Transmitter Current (mA)
Purple Trace is Receiver Current (mA)

SA380TX Configuration

4-20mA Output:

This requires connection of the 4-20mA output to an analogue channel on the SA380TX. Please see VTi21 Hardware Wiring for 4-20mA Operation and follow the instructions titled "Wiring for 4-20mA Operation".

To configure the analogue channel of the SA380TX to accept the 4-20mA output of the VTi21 the web config tool should be used.

To do this, firstly connect to the SA380TX over ethernet, then open a preferred web browser and type [SA380TX IP]/config into the URL. This should open the web config tool.

Next navigate to the real channels tab, as shown below.

Apply the suggested settings shown below to the analogue channel that is connected to the VTi21 4-20mA output.

RS485:

For information on the wiring required for RS485 communications please see VTi21 Hardware Wiring for RS485 Operation and follow the instructions titled "Wiring for RS485 Operation" or "Alternate Wiring for RS485 Operation" dependant on the SA380TX's hardware configuration.

To configure the VTi21 over RS485, please follow the instructions under the heading "Configuration on RS485" in the VTi21 Configuration guide.

After configuring the RS485 connection, each reported channel needs to be assigned to an analogue channel using the settings shown below.

See the table in the Reed VTi21 Outputs for the units and change threshold for each channel.

Installation

To monitor the performance of a Reed track circuit, the current flowing from the rails to the filter module must be monitored.

This feed must pass through the current transducer connected to the "CH1" input on the VTi21.
If monitoring of an additional Reed track circuit is required, the second device must be connected through the current transducer connected to the "CH2" input on the VTi21.
The CT should be placed around one of the wires leading from the "rail" termination to the filter unit.
This is true for both Transmitter and Receiver configurations.

The 4-20mA output of the VTi21 only reports current for CH1.

Please observe that as this is an AC application the device operation is unaffected by the direction that the wire is fed through the current transducer.

Reed VTi21 Outputs

The Reed VTi21 sensor can output the following quantities when monitoring Reed receivers.

VTi21-Reed

Slave Channel	VTi21 Input Channel	Quantity	Description	Typical Range	Units	Suggested AoC
1	1	CH 1 Frequency	Simple Frequency Measurement (zero crossings)	0 to 5000	Hz	1
2	1	CH 1 Total Current	Total current measured in the reed relay frequency range (4-20mA Output)	0 to 5000	mA	10
3	1	CH 1 - channel 211	Total Current at 363Hz	0 to 5000	mA	10
4	1	CH 1 - channel 212	Total Current at 366Hz	0 to 5000	mA	10
5	1	CH 1 - channel 213	Total Current at 369Hz	0 to 5000	mA	10
6	1	CH 1 - channel 214	Total Current at 372Hz	0 to 5000	mA	10
7	1	CH 1 - channel 215	Total Current at 375Hz	0 to 5000	mA	10
8	1	CH 1 - channel 216	Total Current at 378Hz	0 to 5000	mA	10
9	1	CH 1 - channel 217	Total Current at 381Hz	0 to 5000	mA	10
10	1	CH 1 - channel 218	Total Current at 384Hz	0 to 5000	mA	10
11	1	CH 1 - spectrogram / gain	Capture waveform showing the magnitude spectrum of the input signal. Use a "Triggered Capture" to acquire the Spectrogram. note: includes only measured frequencies, which are: 363, 366, 369, 372, 375, 378, 381, 384, 408, 417, 423Hz
12	2	CH 2 Frequency	Simple Frequency Measurement (zero crossings)	0 to 5000	Hz	1
13	2	CH 2 Total Current	Total current measured in the reed relay frequency range	0 to 5000	mA	10
14	2	CH 2 - channel 211	Total Current at 363Hz	0 to 5000	mA	10
15	2	CH 2 - channel 212	Total Current at 366Hz	0 to 5000	mA	10
16	2	CH 2 - channel 213	Total Current at 369Hz	0 to 5000	mA	10
17	2	CH 2 - channel 214	Total Current at 372Hz	0 to 5000	mA	10
18	2	CH 2 - channel 215	Total Current at 375Hz	0 to 5000	mA	10
19	2	CH 2 - channel 216	Total Current at 378Hz	0 to 5000	mA	10
20	2	CH 2 - channel 217	Total Current at 381Hz	0 to 5000	mA	10
21	2	CH 2 - channel 218	Total Current at 384Hz	0 to 5000	mA	10
22	2	CH 2 - spectrogram / gain	Capture waveform showing the magnitude spectrum of the input signal. Use a "Triggered Capture" to acquire the Spectrogram. note: includes only measured frequencies, which are: 363, 366, 369, 372, 375, 378, 381, 384, 408, 417, 423Hz

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