ENMET TDX Series - Manual (Page 7)

TDX-Series ENMET Corporation
5
5.2 Calibration of a Channel
5.2.1 Zero Point Adjustment
T OXIC Z ERO POINT ADJUSTMENT :
Toxic Zero point adjustment is accomplished by exposing the sensor to clean, contaminant-free air for a few minutes.
The signal may be measured, by a standard millivoltmeter located between (PT+) and (PT-) as shown in Figure 1.
Adjust the ZERO ADJUST SCREW to accomplish this reading.
Toxic zero setting: At 0 ppm the signal should read 40mV = 4mA
O XYGEN Z ERO POINT ADJUSTMENT :
It is normally not necessary to adjust the zero adjust screw for oxygen. This may be done to obtain optimum linearity
across the entire range (0 – 30% by vol.), if a new sensor is installed or the zero adjust screw has been accidentally
changed.
To set zero, it is necessary to expose the oxygen sensor to pure 100% nitrogen until a stable reading is obtained. This
can require flowing the nitrogen for 20 to 30 minutes.
Oxygen zero setting: The signal at 100% nitrogen/zero oxygen should read 40mV = 4mA.
5.2.2 Span Calibration Adjustment
A calibration gas is required for span adjustment. A calibration gas is either the same gas which the sensor is designed
to detect or a specified correlation gas. The calibration gas should be at a concentration close to the full scale
concentration of the transmitter range. Calibration gases may consist of gas cylinders, kit generated gases, permeation
tube-generated gases, etc.; any of these are acceptable, as long as the concentration of the gas is known and is close to
the transmitter full-scale concentration.
To perform the span adjustment, the calibration gas is introduced to the sensor at a low, constant flow rate (0.5 liters
per minute).
After 1-2 minutes, the SPAN ADJUST SCREW located inside the transmitter is adjusted so the signal measured
between (PT+) and (PT-) can be obtained by using the formula shown.
(
( )
+ 4
)
x 10 = mV Across (PT)
Toxic Example: Calibrate a hydrogen sulfide transmitter to a range of 0 – 100 ppm using a calibration gas concentration of 100 ppm:
(
( )
+ 4
)
x 10 = 200 mV Across (PT)
Oxygen Examples:
1. Calibrate an oxygen transmitter to a range of 0 – 30% B.V. using a calibration gas concentration of 19.5% B.V.:
(
( )
+ 4
)
x 10 = 144 mV Across (PT)
2. Calibrate an oxygen transmitter to a range of 0 – 30% B.V. using clean fresh ambient air ,20.9 by volume: The
signal at 20.9% B.V. should read 151.5 mV = 15.1mA.
5.2.3 Applying Calibration Gas
To apply calibration gas, carry out the following steps:
1. Apply the test gas of known concentration to the sensor using the calibration adapter provided (See Figure 3.).
2. Wait for a stable reading to be obtained. (1-2 minutes is a suitable period of time).
3. Adjust the SPAN ADJUST SCREW (See Figure 1) until the correct reading across (PT+) and (PT-) is shown.
4. Remove the calibration gas and adapter.
5. Calibration is now complete.
16 x (Gas Concentration)
Range of Sensor
16 x 100
100
16 x 19.5
30