TGS2442 Datasheet, PDF (13/25 Pages) List of Unclassifed Manufacturers – Detection of Carbon Monoxide

5. Circuit Examples
5-1 Basic circuit including trouble detection
TECHNICAL INFORMATION FOR TGS2442
Figure 22 - Basic circuit (including trouble detection)
5-2 Calibration and temperature/humidity compensation
Figure 23 - Calibration & temperature compensation
S-In
8-bit A/D input port
H-In 8-bit A/D input port
R-In
8-bit A/D input port
(Each of these ports acquires data at preset timing.)
RL1,RL2
Pulse
Temp
Calb
open drain output port
open drain output port
open drain output port
open drain output port
Circuit voltage (Vc) across the sensor is applied when RL1 or RL2
ports give the Low (L) output signal at preset timing.
V1
V2
V3
V4
V5,V6
sampling voltage for gas detection
sampling voltage for sensor element trouble detection
sampling voltage for reference voltage
sampling voltage for temperature compensation
sampling voltage for detecting heater circuit breakage
V1 and V2 are acquired during the last half of the 5msec VC pulse
(the first half of the VC pulse is considered as the transient period).
V5 is acquired during heater OFF, and V6 is acquired during heater
ON pulse.
RA = 50% of Vc at the targeted gas concentration
RB = 200-300kΩ
RC = 10kΩ
RD = 20kΩ
RE = 10kΩ
VRadj = 100kΩ
Thermistor: R (25˚C) = 10kΩ, B constant = 3400
Sensor resistance (Rs):
Rs =
Calibration resistance
(RCalb):
RCalb =
Coefficient for temp.
compensation (KTemp):
5 - V1
V1
5 - V3
V3
KTemp =
5 - V4
V4
Operation state:
State
Normal
Alarm
Sensor malfunction
Heater malfunction
Conditions
Rs x KTemp > RCalb and V2 ≥ 0.5V
Rs x KTemp ≤ RCalb and V2 ≥ 0.5V
V2 < 0.5V
V5 ≥ 0.1V or V6 ≤ 4.5V
Revised 03/00
11