Warning
Electrostatic Discharge Required: Always discharge static electricity from your person by touching metal prior to handling any hardware. Failure to do so may result in damage to devices.
Issue
Using sensors, other than the D?T range in a Sigma controller
Product Line
Satchwell Sigma
Environment
- Sigma Release 4_05-SEB (Build 3_43_18)
- Sigma Release 4_05-SP2 (Build 3_42_48)
- Sigma Release 4_06 (Build 3_44_14)
- Sigma Release 4_06 SP1 (Build 3_44_16)
- Sigma Release 4_07 (Build 3_45_48)
- Sigma Release 4_07-SP1 (Build 3_45_51)
- Sigma Release 4_07-SP2 (Build 3_45_58)
- Sigma Release 4_08 (Build 3_46_57)
Cause
Using 10k Type 2 and type 3 Thermistor causes hardware alarm
Resolution
The lookup value for a Sigma resistance input is calculated as a percentage of a 2 volt signal (that's what is measured at the A/D convertor).
If using a sensor other than a standard D?T range sensor, a calculation needs to made, to obtain the value to be entered in the input column (a % of 2 volts) of the look up table.
The calculation is as follows: -
( 10^6 * R1 ) /4000
( 14700 + R1 )
Where R1 = resistance of the input
14700 =resistor on AI card
The circuit shown below is a typical example of an AI channel for a resistance input.
It is suggested to put a 10K resistor in parallel therefore, the resulting circuit resistance can never be higher than 10K.
Attached is information for both the 10K type 2 and 10K type 3 sensors.
Column C is the raw sensor resistance.
Column D is the controller input resistance with a 10K shunt resistor connected.
Column E and F example of the look up table.
