Ion Science MiniPID - Manual (Page 16)

MINIPID 3PIN MANUAL Ion Science Ltd
Page 16 of 27
Unrivalled Detection. www.ionscience.com
Intrinsic Safety
Summary for use of the MiniPID in intrinsic safe applications.
Maximum temperature for intrinsically safe operation.
MiniPID is designed to have minimum response change over their full temperature range, and because
performance of potting compounds changes with temperature, there is no potting compound in the sensor.
However this meant serious design considerations were imposed on the MiniPID for its T4 temperature
rating, due to the lack of internal space for components capable of operating at the 55

C for 1.1 W T4 class
(60

C for 1.0 W and 65

C for 0.9 W).
The MiniPID may be plugged directly into an LEL sensor PCB position whose power is supplied by an
external 125 mA fuse for a T4 rating in an ambient temperature of up to 55

C. The MiniPID is not rated
above the power ratings given for the temperature limits because the internal zener diodes would exceed
their rated temperature rise based upon the 3W zeners’ die temperature rating at the stated maximum
ambient temperature when tested at the fused clamped current.
Summary for use of the MiniPID in intrinsic safe applications.
1. External supply surge current must be limited to 3.3 A under fault conditions.
2. Depending upon maximum supply voltage, the MiniPID may use a 125 mA fuse in the supply line for
55

C for 1.1 W T4 and a series resistor for reduced power limits for operation above 55

C ambient
temperature.
3. Take note of the various maximum supply voltages that may become connected to any of the pins
under fault conditions.
4. Take note of the power limits of the various pins under fault conditions.
5. The capacitance is low and should not cause problems at these voltages.
6. If processing electronics are located in another zone, then barrier/ segregation resistors are required
in any signal lines.
7. Competent third party assessment is required on the final product.
8. MiniPID Reg
Working near 10V should have signal and power rails infallibly isolated to ensure lumped
capacitances on an external short circuit does not exceed the safety current limit.
Possible Intrinsically safe installations Equivalent Intrinsic Safe circuit
Version MAY 2010