UM71 Applications

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 it is recommended that the web config tool 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.

Feel free to rename the channel as you see fit.

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 UM71 VTi21 Outputs for the units and change threshold for each channel.

Again, feel free to rename the channel as you see fit.

Installation

To monitor the performance of an UM71, the current flowing to the REC. 1 connections on the receiver must be monitored.

This feed must pass through the current transducer connected to either "CH1" input on the VTi21.

If monitoring of an additional UM71 receiver is required, the feed connecting to REC. 1 of the second receiver must pass through the current transducer connected to the "CH2" input on the VTi21.

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

Ensure that the current transducers used for UM71 applications are correct. Although they have the same part number as the transducers used in other VTi21 applications, the type required for UM71 must state that they are 40K BURDEN.

See the image below for further clarification.

The wire connecting to R1 on the UM71 receiver must be fed through the current transducer with 2 turns of wire.

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.

UM71 VTi21 Outputs

The UM71 VTi21 sensor can output the following quantities when monitoring UM71 receivers.

Quantity	Units	Change Threshold	4-20 mA	RS485	Description
CH1_UM71	Hz	1			Lock-on frequency of the monitored track circuit. (1700, 2000, 2300 or 2600 Hz)
CH1_ICent	uA	20			The vector sum of the upper and lower sideband currents - Updated 4 times a second
CH1_SBRT	%	5			The ratio of upper to lower sideband current. - Updated once every 4 seconds whilst the track is clear.
CH1_Freq	Hz	50			The transmitter center frequency - Updated once every 30 seconds whilst the track is clear.
CH1_ITot	uA	100			Total RMS current seen by the receiver Updated 4 times a second
CH1_1700	uA	100			Total RMS current in the Upper, Lower and center 1700 Hz bands.
CH1_2000	uA	100			Total RMS current in the Upper, Lower and center 2000 Hz bands.
CH1_2300	uA	100			Total RMS current in the Upper, Lower and center 2300 Hz bands.
CH1_2600	uA	100			Total RMS current in the Upper, Lower and center 2600 Hz bands.
CH1_FFT		Not normally acquired			In real-time reports the gain setting of VTi21 (1 to 32). When used as a "Capture Channel" in a triggered capture event, reports a partial spectrogram of the signal seen by the receiver.
CH2_UM71	Hz	1
CH1_ICent	uA	20
CH1_SBRT	%	5
CH2_Freq	Hz	1
CH2_ITot	uA	100
CH2_1700	uA	100
CH2_2000	uA	100
CH2_2300	uA	100
CH2_2600	uA	100
CH2_FFT		Not normally acquired