Introduction
Based on CQA (HV) information, many engine failures in T-72 are due to either low oil pressure or high coolant temperature (and coolant fan not working). Though the temperature gauge and oil gauge have been provided on the driver instrument panel board to monitor oil pressure and engine coolant temperature, it was felt that driver could not pay attention due to posture of the driver while driving.
Hence it was felt that such a device should be introduced which will draw the attention of driver and take remedial measure to save the engine.
An AVWD (Audio Visual Warning Device with Real Time Clock) consists of temperature sending unit for coolant temperature, pressure switch for engine oil pressure and control panel for audio-visual warning. Seven-segment display is used to display real time. Toggle switch is provided to set the device according to coolant used (water/anti-freeze). The audio warning (100 db) and visual indication will be operative when the coolant temperature reaches up to 115(-3)OC for water as a coolant or 105(-3)OC for antifreeze as a coolant and low engine oil Pressure below 4.5(+0.25)kg/cm2. If in case the audio warning is not required, then Stop Sound switch is provided on control panel to stop the sound for approx. 60 sec.
Block Diagram
The System consists of following:
Temperature sending Unit
Pressure switch
Fan Neutral Signal Input.
Control Panel unit
- Logic and Conditioning unit
- Buzzer for Audio Indication
- Stop Sound Switch
- Water/Antifreeze Selection Switch
- 24-Hour Digital Clock
Display Unit
Visual Display windows
DC Supply 24V (±10%)
Block Diagram Description
A] Temperature sending unit:
The temperature sending unit is used in the system for sensing the temperature when engine is filled with normal coolant or antifreeze coolant. The temperature-sending unit is of PT-100 types with 2-pin male Military Grade connector, encapsulated in stainless steel body. The sending units are highly reliable, accurate, and durable. The resistance value of the temperature unit changes as per temperature variation. The resistance – temperature characteristic is linear throughout its operating range.
B] Pressure Switch:
The pressure switch used in the system is electro-mechanical type. For increase and decrease of pressure there is mechanical motion. The mechanical motion operates the electrical snap switch, which is inside the pressure switch assembly. The set point is pre-set at factory end at 4.5Kg/cm².The pressure switch is in brass body.
C] Fan Neutral Status:
The status of cooling fan (Engaged/Neutral) is sensed by tapping the electrical connection from existing fan neutral switch.
CONTROL UNIT:
C] 24-Hour Digital Clock:
A 24-hour digital clock is provided on control panel of Audio Visual Warning Device. Bright red coloured 7-segment LED’s are used for clock display. User can set Hour/Minutes using keys provided on control panel. To set required hours press SET key and increment hours key similarly to set required minutes press SET key and increment minutes by MINUTES key.
As soon as the power (24V DC) is given to control panel digital clock will display the current time.
To set Hours, Keep Set key pressed and press Hours key to increment hours. Similarly keep Set key pressed and press Minutes key to increment minutes.
D] Logic and Conditioning Unit:
Logic unit is an intelligent device, which monitors low engine oil pressure, fan neutral condition as well as coolant temperature (water /antifreeze). Logic Unit checks all these parameters in their safe ranges, if any of the previously described parameters is invalid then the corresponding Audio Visual indication is activated.
E] Water and Antifreeze Coolant Selection Switch:
It is a dust protected switch mounted on the panel. This switch provides a selection for a coolant (Water/Antifreeze) as per requirement.
F] Buzzer For Audio Indication:
Buzzer used in the system is good enough in any environmental situation having sound output about 100db.It is common for all three parameters monitored by the system.
G] Stop Sound Switch:
It is dust proof switch, used to deactivate the output of the buzzer. It consists of Push to On button switch on the control panel, by pressing this switch buzzer sound stops whenever required.
DISPLAY UNIT
H] Visual Display Window:
For visual indication there are three display windows on display unit. First window indicates High coolant temperature (Water/Antifreeze), second window indicates low oil pressure, and third window indicates fan neutral indication. Each display window consists of bright RED coloured LEDs.
System Operation
When the Power (24V±10% DC) is given to the system the system operate after seven seconds delay.
Select the mode with water/antifreeze selection switch depending on the type of coolant used.
The warning will be operative when the coolant temperature reaches up to (115˚C - 3˚C) for water coolant and (105˚C - 3˚C) for antifreeze coolant. High coolant temperature indicator window starts blinking along with an audio buzzer.
When the engine oil Pressure falls to 4.5kg/cm² the Low Oil pressure window starts blinking along with Buzzer.
When the radiator Fan is at neutral position window starts blinking along with Buzzer.
If in case the audio alarm is not required, the stop sound facility is provided on the control panel with a timer function, which mutes buzzer for 60-sec.
Salient Features
- The system is fully solid state. This improves functional accuracy and reliability of the system, which monitors the current temperature cooling, fan status and pressure signal, checks both for the safe range.
- The regulated power supply unit protects the controller circuit from voltage fluctuations as well as reverse polarity connection. The system can work on supply voltage of 24V ± 10%.
- Red coloured LED’s are used instead of bulbs. As a result failure of bulb is eliminated.
- RTD (PT-100) type sending unit with 2-pin Military-Grade connector is used. This sending unit is linear and accurate. To improve life of sending unit the sensor is encapsulated in Stain less steel body.
- Pressure switch used is having brass body with 3-pin Military –Grade connector, which can withstand pressure up to 150 bar.
- Dust protected switches are provided for ‘Stop sound’ and ‘Coolant selection’.
- A digital clock is provided on AVWD control panel.
Assembly Instruction
Audio visual Warning Device consists of
1. Control panel with mounting bracket
2. Display Unit.
3. Temperature sending unit with copper washer
4. Pressure switch
5. Power supply harness
6. Control panel harness
7. Sending unit harness
8. Four way connector
9. Blinding plug.
AVWD Kit Assembly:
i) AVWD – Display Unit:
1. Remove Drivers Control panel.
2. Remove dummy plate at top right corner of the panel.
3. Fix Display unit and front plate as indicated in drawing no.ESSPL/AVWD-T72/009.
4. Fix display Module Harness assembly (Part No. ESSPL/AVWD-T72/008) by connecting 4 way
connector to display unit.
5. Re-assemble drives control panel to its position.
ii) AVWD – Control Panel:
1. Locate the Control Panel as shown in Drg. No. ESSPL/AVWD-T72/010
Assuring that the rubber grommets are in place.
2. Fix Display Module Harness (Part No.ESSPL/AVWD-T72/008)
Control Module Harness (Part No.ESSPL/AVWD-T72/003 and
Power Supply Harness (Part No. ESSPL/AVWD-T72/007)
3. Make interconnections of control module harness with Pressure switch Harness,
Fan Neutral Harness and Temperature Sending unit Harness.
iii) Pressure Switch Assembly:
1) Remove existing hose connection to the existing pressure switch.
2) Attach the 4 – way connector port no-1 to the existing pressure switch as shown in drawing No:ESSPL/AVWD-T72/015.
3) Attach the hose assembly to the 4 – way connector at port no-2 as shown in drawing.
4) Screw the blinding plug at port no-3 of the 4 – way connector.
5) Attached the Pressure switch No: ESSPL/AVWD-T72/011at port no-4 of the 4-way connector No: ESSPL/AVWD-T72/013.
6) Don’t over tight 4-way connector.
7) Don’t over tight pressure switch.
8) Don’t forget wire locking.
iv) Temperature Sending Unit assembly:
1) Remove the blinding plug on the engine coolant pipe (at Extra port).
2) Fix PT-100 with connector (ESSPL/AVWD-T72/014) at extra port on coolant pipe with cooper- asbestos washer in place.
3) Fix temperature Sending Unit Harness Assy. (Part No. ESSPL/AVWD-T72/004) to
PT-100.
4) Suitably route the cable up to driver’s compartment.
v) Fan Neutral Connection:
1) Tap Fan Neutral connection from switch fitted on fan neutral mechanism using Fan
Neutral Harness assembly.(Drg.No. ESSPL/AVWD-T72/006).
2) Route the cable suitable up to driver’s compartment.
Part List
Items fitted in the Audio Visual Warning Device kit
1 Control panel ESSPL/AVWD-T72/010 1
2. Display unit ESSPL/AVWD-T72/009 1
3. Pressure switch with washer ESSPL/AVWD-T72/011 1
4. Temperature sending unit ESSPL/AVWD-T72/014 1
5. 4-way connector ESSPL/AVWD-T72/015 1
6. Blinding plug with washer ESSPL/AVWD-T72/012 1
7. Cable harness assembly for control panel ESSPL/AVWD-T72/003 1
8. Cable harness assembly for power supply ESSPL/AVWD-T72/007 1
9. Cable harness assembly for display module ESSPL/AVWD-T72/008 1
10. Asbestos copper washers ESSPL/AVWD-T72/017 1
Trouble Shooting
1 Digital clock will not display the current time.
Ensure proper connections.
Measure voltage in 2-pin female connector it should be 24VDC ± 10 %.
2 Stop sound switch and Water/Anti toggle switch not operating.
Remove the dust cover and fit it properly
3 High coolant temperature indicator window start blinking.
Ensure proper connections of sensor harness.
Required Tools
1 Temperature Sending Unit a) Spanner No: 22
b) Pliers
2 Pressure Switch a) Spanner No: 24
b) Pliers
3 Control Panel a) Spanner No: 10
4 Display Unit a) Spanner No: 07
5 Harness Routing a) Spanner No: 10
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