Honeywell UDA2182 manual Example of a Conductivity Loop

Appendices

15.2Appendix A – Entering Values for Lead Resistance Compensation

(See Appendix B for titanium cells mounted into stainless steel flow chamber 31079198)

Introduction

If you use standard Honeywell cell lead lengths of 7 or 20 feet connected directly to the Analyzer, no compensation for lead resistance is necessary. Similarly, if a junction box is used to extend the leads up to 150 feet, no compensation is required. However, if longer leads are used (greater than 150 feet), signal accuracy can be adversely affected unless you enter information that will permit the UDA2182 to compensate for lead resistance in the black and white cell leads only. Lead resistance compensation is not necessary, nor applied to the other cell leads.

For lengths up to 1000 feet*, simply specify the gauge and length as described in Table 6-5. Note that the maximum wire size for sensor inputs at the input terminal board is 16AWG.

*DirectLine DL4000 series cells have a total lead length limit of 250 feet.

If mixed wired gauges are used, or lead length or wire gauge are not within the stated ranges, the UDA2182 can still perform the compensation. However, you must first calculate the lead resistance, and then put it in terms of the available settings for AWG gauge and length.

The resistance of each available gauge choice (in copper wire) is: 16 AWG = 4.0 ohms per 1000 feet

18 AWG = 6.4 ohms per 1000 feet

20 AWG = 10.2 ohms per 1000 feet

22 AWG = 16.1 ohms per 1000 feet

For example, suppose extension cables between the cell and Analyzer consist of 500 feet of 18-gauge wire and 200 feet of 16-gauge WIRE. The cell has the TC head option.

500 ft of 18 AWG wire

Analyzer

Junction

Box

200 ft. of 16 AWG wire

Honeywell

Conductivity Cell

Figure 15-1 Example of a Conductivity Loop

Because there are two different types of wire used in each lead to the cell in this example, the total lead resistance is calculated as follows: (Note: the analyzer accounts for the fact that there is always a pair of conductor wires in the system loop.)

(0.5 x 6.4) + (0.2 x 4.0) = 4.0 ohms

200 UDA2182 Universal Dual Analyzer Product Manual January 2009