Checking The Display - Messko ZT-F2 Instrucciones De Montaje Y Servicio

5.2 Option: 4 – 20 mA analogue output
The ZT-F2 can be supplied with a 4 – 20 mA analogue
output, rather than the Pt100 measuring resistor. In this
case, the connecting cable has two wires and the max. R/L
is 750Ω at 24 V DC. (See page 12, figure 7 for the terminal
connection diagram)
May be equipped with two
Optional
analogue outputs
6. Setting the temperature gradient
6.1 Calculating the resistance for setting the
temperature gradient
The following values are specified in the transformer
design data:
I = Transformer current
K = Temperature gradient
Thus, we can calculate:
I = Heating current
h
The parallel resistance for heating is calculated using the fol-
lowing formula:
Formula:
6.2 Heating current I table
h
K I
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
Fig. 2
6.3 Setting diagram
Fig. 3
4,4 x I
h
R =
I-I
h
mA/mV
h
740
800
860
920
980
1040
1090
1140
1190
1240
1280
1320
1360
1400
1440
Sample calculation 1:
K = 20
I = 1950 mA
I = 1040 mA
h
I-I = 910 mA
h
4,4 x 1040
R =
910
= 5,03Ω (5Ω)
6.4 Setting the temperature gradient in
the ZT-F2
If you open the cover of the ZT-F2, you will see the
terminal board (page 12, fig. 7). The setting diagram
(fig. 3), setting table (fig. 2) and calculation formula are
printed on the inside of the cover.
Insert the plug-in jumper to determine the partial resistance
(R) as calculated under point 6.1.
1. Attach the plug-in jumper to either A-B, A-C or A-D:
If R < 16Ω, then place jumper across A-B
(i.e. series resistance = 0Ω)
If R ≥ 16Ω, then place jumper across A-C
(i.e. series resistance = 16Ω)
If R ≥ 36Ω, then place jumper across A-D
If R ≥ 90Ω, then leave all the plug-in jumpers open.
2. Remove the top plug-in jumper to determine the
residual resistance:
If all the jumpers are closed, then the residual
resistance should be 0Ω
If all the jumpers are open, then the residual resistance
should be 15.66Ω
3. Park any plug-in jumpers that are not required in the
holes provided on the left.
4. Measure the heating current:
Attach the millivoltmeter to terminals 7 – 8.
(The measurement is taken via 1Ω, so mV = mA).
5. Any necessary corrections can be made using the
0.33Ω resistors.
6. Use an indelible felt-tip pen to write the settings in
the corresponding boxes on the terminal board.
PRACTICAL TIP !
Set the heating resistance before fitting the ZT-F2
transformer temperature transmitter.
IMPORTANT !
Check that the conditions specified under point 2
(Installation conditions and testing) are fulfilled be-
fore you carry out any comparative measurements
or tests.

7. Checking the display

Allow the pointer-type thermometer to warm up for 30
minutes and then compare the readings on the dial and the
electronic display. The readings should lie within the
tolerance ranges of both devices.
8. Service
If the above instructions are not sufficient, please contact
our factory.
9. Maintenance
The ZT-F2 transformer temperature transmitter is
5
English
Sample calculation 2:
K = 30
I = 1535 mA
I = 1280 mA
h
I-I = 255 mA
h
4,4 x 1280
R =
255
= 22Ω