Emerson Process Management 381 instruction manual Temperature vs Resistance of Auto, Element

MODEL 381pH/ORP

3.4PREAMPLIFIER TROUBLESHOOTING. To deter- mine if the preamplifier is operable, proceed as follows:

1.	Remove the sensor from process.
2.	Remove the cover from the body by grasping the

SECTION 3.0

MAINTENANCE

TABLE 3-2

TEMPERATURE vs RESISTANCE OF AUTO

T.C. ELEMENT

	body and rotating the cover 1/4 turn in the count-
	er-clockwise direction.
3.	When the cover breaks loose from the body, pull
	straight out on the cover to expose the com-
	ponents attached to the body and disconnect the
	BNC connector from the preamplifier, leaving the
	cable connected. Inspect the internal preamplifier
	area for signs of moisture or corrosion; moisture
	can short out the preamplifier. Dry all parts thor-
	oughly before testing.
4.	Short the center pin of the BNC on the preamp-lifi-
	er to the outside of the BNC connector.
5.	The meter indication should be approximately
	center scale (7 pH).
6.	If the meter indication is not as specified in Step 5,
	proceed to the transmitter instruction manual for
	further troubleshooting. If the transmitter is opera-

Temperature °C

0

10

20

25

30

40

50

60

70

80

90

100

Resistance

(Ohms) ± 1%

3K PT-100

2670 100.0

2802 103.8

2934 107.7

3000 109.6

3066 111.5

3198 115.4

3330 119.2

3462 123.1

3594 126.9

3726 130.8

3858 134.6

3990 138.5

	ble with the preamplifier bypassed, then the pre-
	amplifier is defective.
7.	Unplug the preamplifier from the body.
8.	Plug a new preamplifier into the body.
9.	Plug the BNC connector of the glass electrode into
	the preamplifier.
10.	Make sure all O-rings are clean, lubricated and in place.
11.	Plug the cable connector into the preamplifier, making
	sure the cable is towards the center of the body.
12.	Install the cover on the body so that the threads
	engage.
13.	Rotate the cover until the triangle on the body
	aligns with (or falls within) the adjacent mark on
	the cover.

CAUTION

DO NOT use a pipe wrench on the body or cover. Severe damage could result.

14. Install the sensor as described in Section 2.0.

3.5T Automatic Temperature Compensator. The temper- ature compensator element is temperature sensitive and can be checked with an ohmmeter. Resistance increases with temperature.

The 3K element will read 3000 ohms ± 1% at 25°C (77°F) and a Pt-100 will read 110 ohms. Resistance varies with tem- perature for a 3K and Pt-100 element and can be determined according to Table 3-2 or the following formula:

RT=Ro [l+R1 (T-20)]

Where RT = Resistance

T = Temperature in °C

Refer to Table 3-3 for Ro and R1 values

TABLE 3-3

Ro and R1 VALUES FOR TEMPERATURE

COMPENSATION ELEMENTS

Temperature	Ro	R1
Compensation Element
3K	2934	.0045
PT-100	107.7	.00385

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