Practical Boat Owner - February 2016

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Gear

Oil pressure

The new sender has two terminals, the resistive sender which is wired

back to input A1 and the loss of pressure alarm switch terminal which

has the original wire reconnected.

The set-up utility is now used to configure the channel: firstly we select

‘port’ engine (instance 0, the default for a single engine). It then allows A1

to be set to Oil Pressure and the current source turned ON. The sender

voltage at zero pressure can be read from the terminal viewer window,

with the engine switched off.

This gives:

Sense volts 1 (the sender voltage) = 0.1V

Field value 1 (the oil pressure) = 0 psi

For the high-pressure value, as this is a new sender, we will have to rely

on the manufacturer’s data sheet to calculate this, and the fact that

NoLand Engineering quote their constant current as around 9mA. Taking 7

Bar (100psi) at start-up, the manufacturer quotes a sender resistance of

1191 , resulting in a sender voltage of 1.07V (119 1 x 0.009A).

This gives the high value:

Sense volts 2 = 1.07

Field value 2 = 100 psi (7 Bar converted as I prefer pressure in psi).

Finally, set the alarm value to 00 to disable as the original alarm is

still connected.

Coolant temperature

The graph shows how temperature sender characteristics are non-linear

so a choice of operating point has to be made, accepting that away from

that point the reading becomes less and less accurate. This actually isn’t a

problem, as the only temperature of real interest is the 60°C -70°C normal

operating region. If things go wrong and temperature rises, it will show up

NoLand RS11 Engine Data Converter

The NoLand RS11 has six configurable input channels and two pulse-type

channels. It comes with a set-up utility software package and a USB lead

to link your computer to the device. The set-up utility allows each channel

to be configured to output a particular type of data and to set the

calibration of the sender connected to the channel.

Channel allocation

A1 Oil pressure

A2 Coolant temperature

A3 Fuel tank level

A4 Domestic consumption current

A5 Charging current

A6 Battery 2

P1+/- Engine revs

P2+/- Not used

Engine hours are automatically

logged, and you can set the

existing engine hours into the

RS11 (as its starting point) via the

set-up utility. The unit is supplied

from 12V or 24V, and the 0V is

connected to the newly-installed

instrumentation 0V bus.

Sender calibration

The oil pressure, coolant temperature and fuel level senders are resistive,

and to create a voltage at their terminal they require a small constant

current passing through them. If the current remains constant, then (by

Ohm’s law) the voltage at the terminal will be proportional to the resistance

which, of course, is determined by the oil pressure, coolant temperature

or fuel level. The constant current is provided by the RS11 channel

itself. (If piggybacked off an existing instrument, that will provide the

constant current.)

How the set-up utility works

An assumption is made in the RS11 that the relationship between

the parameter being measured and the voltage seen at the sender is

a linear one. To set this up we need to configure low and high end

operating points, and the RS11 will ‘draw’ a straight line relationship

between them. This works well for the oil pressure and the fuel sender, but

is a limitation with the temperature sender. The utility helps by displaying

the voltage at the sender connected to each channel in the ‘terminal

viewer’ window. The pulse channel (P1+/-) is calibrated by entering a

multiplier in the port RPM box.

RS11 fully installed and connected

to the Raymarine backbone via the

DeviceNet to STNG cable adapter

Sender voltages displayed in the ‘terminal viewer’ window

Temperature sender’s non-linear characteristics

RS11 set-up utility

RS11 over-temperature alarm set via the utility software.

This is set to around 85°C as an early warning