Instruction manual

MODEL XMT-A-FF/FI SECTION 12.0

CALIBRATION - MONOCHLORAMINE

12.2 PROCEDURE — ZEROING THE SENSOR

1. Place the sensor in the zero standard (see Section 10.1). Be sure no air bubbles are trapped against the mem-

brane. The sensor current will drop rapidly at first and then gradually reach a stable zero value. To monitor the

sensor current, go to the main display and press  until the input current screen appears. Note the units: nA

is nanoamps, µA is microamps. Typical zero current for a monochloramine sensor is between 0 and +20 nA.

A new sensor or a sensor in which the electrolyte solution has been replaced may require several hours (oc-

casionally as long as overnight) to reach a minimum current. DO NOT START THE ZERO ROUTINE UNTIL

THE SENSOR HAS BEEN IN ZERO SOLUTION FOR AT LEAST TWO HOURS.

2. Press MENU. The menu screen appears. Choose Calibrate.

3. Choose Chlorine.

4. Choose Zero.

5. The screen at left appears. The top line is the raw sensor current.

6. Once the reading is stable, the screen at left appears. Sensor zero is

complete and the transmitter has stored the zero current. The screen

remains until the operator presses MENU then EXIT to return to the

main display.

NOTE

Pressing ENTER during the zero step will cause the transmitter to

use the present sensor current as the zero current. If the sensor is

zeroed before the current has reach a minimum stable value, sub-

sequent readings will be in error.

7. This screen appears if the zero current is extremely high. See Section

15 for troubleshooting. To repeat the zero step, press EXIT and choose

Zero.

8. This screen appears if the zero current is moderately high. To continue,

choose Yes. To repeat the zero step, choose No. See Section 15 for

troubleshooting.

Cal?

Chlorine

Temp

Cal?

InProcess

Zero

Live 200nA

Zeroing

Wait

Sensor Zero Fail

Current too high

Possible ZeroErr

Proceed? Yes No

Calibrate

Sim. PV

Program Display

Live 0.000ppm

Sensor Zero Done