056 092 Best Practices for Wiring Resistive Sensors

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Author: J.Z. Page 1 of 4 056-092 ISSUE: 1 
 
 
 
 
 
Recommended Practices for Wiring 
Resistive Sensors 
 
1 OVERVIEW 
 
This training document is intended to assist with wiring resistive sensors to DSE modules. Outlined below are the DSE 
recommended wiring practices, as well as examples of common mistakes made when installing sensors. It is 
assumed that all personnel carrying out the work described have a sufficient level of technical knowledge to assess 
and complete the job to a competent level. 
 
 
2 INCORRECT WIRING PRACTICES 
 
Connecting a resistive sensor to a DSE controller appears at first to be a straightforward procedure. There are, 
however some common practices which may inadvertently lead to erroneous sensor readings or a complete loss of 
sensor data. In particular, the wiring configuration of the ground and sensor common connections may affect readings. 
This is illustrated in the diagram below: 
 
 
To calculate the displayed 
values of resistive sensor 
inputs, the DSE module 
applies a fixed current to 
the Analogue Input circuits, 
and measures voltage at 
each active Analogue Input 
terminal with respect to the 
Analogue Input Common 
terminal. In this example 
the earth terminal of the 
Coolant Temp Sensor is 
wired to the battery 
negative common circuit. 
Configured as such the 
sensor is susceptible to 
voltage changes in the 
negative circuit, and will 
show erroneous readings 
when such changes take 
place. 
High Impedance 
in the Analogue 
Input Common 
cable causes a 
voltage 
difference with 
respect to earth. 
Damaged, low 
quality or 
excessively long 
cables all lead to 
this. 
Analogue Input Common is 
connected to the same circuit as a 
battery charger’s negative terminal. 
When the charger is active, the 
return current causes a voltage 
increase in the circuit. As with the 
Coolant Temp Sensor example, a 
change in negative circuit voltage 
leads to incorrect sensor data. The 
difference in this case is; a raised 
Analogue Input Common voltage 
will cause incorrect readings on all 
active resistive sensors. 
 
056-092 ISSUE: 1 Page 2 of 4 Author: J.Z. 
 
3 RECOMMENDED WIRING PRACTICES 
 
NOTE: The diagram shows a generic earthing configuration. For further information on earthing 
conventions, such as floating or positive earth, refer to the relevant DSE operator’s manual. 
 
DSE recommendations for wiring resistive sensors are outlined below in bullet notation. All points are intended solely 
as a guideline, and as such each installation must be evaluated individually from both an operational and safety 
perspective. 
 
o Sensor ground connections wired directly between the sensor body and engine block. 
o Analogue input common used solely as ground reference, and not providing a ground connection for any other 
device. 
o Analogue input common circuit unsusceptible to voltage increase as a result of current flow from another device, 
for example return current from a battery charger. 
o Consideration for the sensor cable lengths, cross-sectional area and quality made to ensure voltage drop across 
the cable remains within acceptable limits. Refer to relevant DSE Operator Manual and manufacturer’s 
specifications for the sensor. 
o Battery negative connected to earth. 
 
A typical example of recommended wiring practices is shown below: 
 
 
 
 
Analogue 
Input 
Common 
wired directly 
to earth point 
with no other 
connections. 
Correctly 
specified 
cable used. 
All sensor ground 
connections wired 
directly to engine 
block. 
 
Author: J.Z. Page 3 of 4 056-092 ISSUE: 1 
 
4 COMMON FAULTS 
 
Other faults commonly associated with resistive sensors are: 
 
o PTFE Tape Around Sensor Threads. Often used to aid sealing, the PTFE tape also acts as electrical insulation. 
This is a problem on resistive sensors designed to use the surface they are screwed into (usually the engine 
block) as the earth connection. The PTFE tape creates a high resistance between the sensor and earth, causing 
incorrect values/loss of sensor readings. 
o Incorrect Washer/Seal Used with Sensor. Similarly to the PTFE tape, the wrong type of washer or seal for the 
selected sensor may cause a high resistance to the sensor common. Manufacturers guidelines must always be 
followed regarding sealing requirements. 
o Sensor Failure. The majority of resistive sensors utilise internal moving parts to provide variable readings. As 
with all moving components, these are subject to wear and will fail in time. Environmental factors such as water 
ingress may serve to additionally shorten the lifespan of such parts. A typical failing resistive sensor may display 
high readings, before becoming permanently open circuit. 
o Poor Termination. Incorrectly terminated sensor wires may cause high resistance, and thus incorrect readings. 
Furthermore, the connections are likely to be weaker and may fail sooner than expected, especially if attached to 
vibrating machinery such as an engine. 
 
 
5 FAIL TO STOP AND THE OIL PRESSURE SENSOR 
 
The Fail to Stop alarm becomes active if a stop command has been issued by the DSE module, and any of the sensor 
values selected for Crank Disconnect are above specified limits when the Stopping Timer has completed. Depending 
on module type and configuration the Crank Disconnect function will read from the following values: 
 
o Oil Pressure 
o Generator Frequency 
o Engine Speed 
o Charge Alternator Voltage 
o Generator Voltage 
 
If the engine is physically verified to have stopped, and the alarm is present, the most likely cause is a fault in the Oil 
Pressure Sensor circuit. This may be due to any of the faults or incorrect wiring practices described elsewhere in this 
document. The Oil Pressure value is checked on the front panel of the DSE module or using the SCADA section of the 
DSE Configuration Suite PC software. Carrying out this quick and easy test may avoid a lengthy fault finding process. 
 
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