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)
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.
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.
