Datasheet

Revised 08/12
4
TECHNICAL INFORMATION FOR TGS3870
1-6 Standard test conditions
Standard test conditions for all data shown in this
brochure were as follows:
Figure 5a - Sensitivity to various gases for methane sensing
(Ro = Rs in 3000ppm of CH4, VH =0.9)
Figure 5b - Sensitivity to various gases for CO sensing
(Ro = Rs in 100ppm of CO, VH =0.2)
0.1
1
10
100
10 100 1000 10000
Methane
Hydrogen
CO
Air
Rs/Ro
Gas concentration (ppm)
0.1
1
10
100
1000
10 100 1000 10000 100000
Methane
Hydrogen
CO
Air
Rs/Ro
Gas concentration (ppm)
Sensor
RS
R H
V H
V C
(+)
(-)
V
RS
(+)
(-)
1
3
2
R
L
Figure 4 - Basic measuring circuit
Preheating of sensor: 5 days
VH (H/L): 0.9V/0.2V (see timing chart, Fig. 2)
VC: 5.0V pulse (see timing chart, Fig. 2)
1.7 Basic measuring circuit
The sensor requires two voltage inputs: heater voltage
(VH) and circuit voltage (VC). The sensor has three
pins: Pin #3--heater (+), Pin #2--sensor electrode (+),
and Pin #1--common (-). To maintain the sensing
element at specic temperatures which are optimal
for sensing two different gases, heater voltages of
0.9V and 0.2V are alternately applied between pins #1
and #3 during a 20 second heating cycle (see Fig. 2).
Circuit voltage (VC) is applied between both ends
of the sensor (Rs) and a load resistor (RL), which are
connected in series, to allow measurement of voltage
(VRS) as shown in Figure 4.
Circuit voltage (Vc) should be applied only at the
moment when the signal is taken from the sensor
(please refer to Fig. 2):
*for methane--5.0V for 5msec. following VH
of 0.9V for 4.985 sec.
*for CO--5.0V for 5 msec. following VH of 0.2V
for 14.985 sec.
Caution: Do not apply a constant circuit voltage
(5.0V) or the sensor would not exhibit its specied
characteristics.
2. Basic Sensitivity Characteristics
2-1 Sensitivity to various gases
Figures 5a and 5b show the sensor’s relative
sensitivity to various gases. Figure 5a shows the
characteristics for methane sensing, while Figure 5b
shows the characteristics for sensing of CO. The Y-axis
for each gure shows the ratio of sensor resistance in
various gases (Rs) to the sensor resistance in 3000ppm
of methane (Fig. 5a) and in 100ppm of CO (Fig. 5b).
As shown by Figure 5a, TGS3870 shows very good
sensitivity to methane and good selectivity when
compared with hydrogen.
Excellent sensitivity to CO is shown in Figure 5b as
evidenced by the sharp drop in sensor resistance as
CO concentration increases. Selectivity is also quite
Rs/Ro
Rs/Ro