SENSOR

The Pt1000 sensor circuit can be tested with substitute resistors. This applies to ALL products. Use standard resistors of the following values:

1200 ohm is 52 deg C

1300 ohm is 78 deg C

1500 ohm is 130 deg C
 

Pt1000 RTD type B grade is used and has a tolerance of +/- 0.5 degree C.

The measurement uncertainty in the circuit used adds an extra 0.5 degree C.

So the readings should be accurate to +/- 1 degree C.

The characteristic is roughly 3.9 ohms per degree C so a test resistor can give a reading 3 degrees out if 1% tolerance. The cable run length is not going to be an issue adding in much less than 1 ohm.

The immersion depth in the rubber pipe is 20mm.

The hole to be drilled is 4.0mm, the sensor is 5.0mm diameter.

To stop water seeping out there is an ‘O’ ring compressed when the band is done up. Also when you assemble the last nut on Sensor type ‘A’ use your silicone sealant on the thread which stops any water ingress through the nut thread.
 

WATERPROOFING

The front panel displays are waterproof. All the electronics circuits are varnished, normal practise with out of doors wet places. The connector boxes are normally under the panels, so in a dry place like the rest of the wiring. Cable runs may have connectors to extend the lengths with exposed wires, this is not normally a problem as the circuits are low impedance and unaffected by leakage. Non-conductive sealant is recommended if you wish to take additional measures, but do allow for servicing.

The SM010 display has the button inside the cover and care should be taken to screw the lid on tight after use. 
 

OPERATION and ALARM SETPOINT

When the engine temperature has stabilised there will be a certain temperature rise from the inlet to the outlet depending on the engine model and how efficient it is. This is used to put the set point 20 deg C away on the lower priced units when you ‘calibrate’. 

When you work the engine hard there will be a lot more power output and a lot more heat generated, but a larger water flow to compensate. So on reducing power the heat is still there to be removed but the flow is reduced so the temperature can shoot up until it stabilises again.

So if you set the alarm point too close to the running temperature you will get false alarms. You are after a critical condition which is completely outside normal operation hence Silicon Marine advises 85 deg C with sea water temperatures around 15 deg C.

NMEA COMMUNICATIONS

The product emits an NMEA0183 sentence for a Transducer (XDR) for temperature. It meets the requirements of V3.01 of the standard. The standard is however fairly ill-defined and using it requires some programmable device to translate at the point you want to see it. For the fourth field of the parameter we send the instrument device type, eg SM022 and A or B to distinguish between the two sensors.

The NMEA0183 standard is now at V4.30 and the fourth field has been tightened up so our product will change to meet the new requirements. The sentences will now have ‘Exhaust#1’ or ‘Exhaust#2’ instead of the product code.

Moving on to the current standard, NMEA2000, it turns out that the temperature can be translated to PGN130316 but there is not a field number for ‘Exhaust Coolant’ or ‘Exhaust Water’. There is one for ‘Coolant’ and one for ‘Exhaust Gas’ so even if you found a bridge device between the two protocols it is difficult to see how you can use it in your engine management system screen without upsetting some sentences already being created by your engine sensors. A bridge device must be used because the communication hardware is completely different, based on CAN which was developed for automotive and boat applications.