PT100溫度變送器的正溫度系數(shù)補(bǔ)償
摘要:本文回顧了通用溫度傳感器的主要特性,重點(diǎn)介紹RTD PT100溫度變送器,并提供了一種簡(jiǎn)單的方法對(duì)PT100輸出信號(hào)進(jìn)行線性化處理和調(diào)理。
溫度是非常重要的物理參數(shù),熱電偶和熱敏電阻(RTD)適合大多數(shù)高溫測(cè)量,但設(shè)計(jì)人員必須為特定的應(yīng)用選擇恰當(dāng)?shù)膫鞲衅?,?提供了常用傳感器的選擇指南。
表1. 傳感器特性
Feature | Thermocouple | RTD |
Response time | Better | |
Maximum temperature | Higher | |
Ruggedness | Better | |
Cost efficiency | Better | |
Accuracy | Better | |
Long-term stability | Better | |
Standardization | Better |
RTD具有較高的精度,工作溫度范圍:-200°C至+850°C。它們還具有較好的長(zhǎng)期穩(wěn)定性,利用適當(dāng)?shù)臄?shù)據(jù)處理設(shè)備就可以傳輸、顯示并記錄其溫度輸出。因?yàn)闊崦綦娮璧淖柚岛蜏囟瘸收汝P(guān)系,設(shè)計(jì)人員只需將已知電流流過(guò)該電阻就可以得到與溫度成正比的輸出電壓。根據(jù)已知的電阻-溫度關(guān)系,就可以計(jì)算出被測(cè)溫度值。
電阻值隨溫度的變化稱為“電阻的溫度系數(shù)”,絕大多數(shù)金屬材料的溫度系數(shù)都是正數(shù),而且許多純金屬材料的溫度系數(shù)在一定溫度范圍內(nèi)保持恒定。所以,熱敏電阻是一種穩(wěn)定的高精度、并具有線性響應(yīng)的溫度檢測(cè)器。具體應(yīng)用中選用哪一種金屬材料(鉑、銅、鎳等)取決于被測(cè)溫度范圍。
鉑電阻在0°C的標(biāo)稱電阻值是100Ω,盡管RTD是一種標(biāo)準(zhǔn)化器件,但在世界各地有多種不同的標(biāo)準(zhǔn)。這樣,當(dāng)同一標(biāo)準(zhǔn)的RTD用在不同標(biāo)準(zhǔn)的儀表設(shè)計(jì)中時(shí)將會(huì)產(chǎn)生問(wèn)題。
表2. 鉑電阻RTD的公共標(biāo)準(zhǔn)*
Organization | Standard | ALPHA (α): Average Temperature Coefficient of Resistance (/°C) | Nominal Resistance at 0°C (Ω) |
British Standard | BS 1904: 1984 | 0.003850 | 100 |
Deutschen Institut für Normung | DIN 43760: 1980 | 0.003850 | 100 |
International Electrotechnical Commission | IEC 751: 1995 (Amend. 2) | 0.00385055 | 100 |
Scientific Apparatus Manufacturers of America | SAMA RC-4-1966 | 0.003923 | 98.129 |
Japanese Standard | JIS C1604-1981 | 0.003916 | 100 |
American Society for Testing and Materials | ASTM E1137 | 0.00385055 | 100 |
*Sensing Devices, Inc.生產(chǎn)滿足上述標(biāo)準(zhǔn)的鉑電阻RTD。
鉑金屬的長(zhǎng)期穩(wěn)定性、可重復(fù)操作性、快速響應(yīng)及較寬的工作溫度范圍等特性使其能夠適合多種應(yīng)用。因此,鉑電阻RTD是溫度測(cè)量中最穩(wěn)定的標(biāo)準(zhǔn)器件。以下公式描述了PT100 RTD的特性,顯然它的溫度與電阻呈非線性關(guān)系:
RT = R0(1 + AT + BT² + C(T-100)T³)
其中:
A = 3.9083 E-3
B = -5.775 E-7
C = -4.183 E-12 (低于0°C時(shí))或0 (高于0°C時(shí))。
表3是表格形式。
表3. 電阻/溫度表**,385鉑電阻,0°C時(shí)為100.0Ω
°C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
-100 | 60.26 | |||||||||
-90 | 64.3 | 63.89 | 63.49 | 63.08 | 62.68 | 62.28 | 61.87 | 61.46 | 61.06 | 60.66 |
-80 | 68.32 | 67.92 | 67.52 | 67.12 | 66.72 | 66.31 | 65.91 | 65.51 | 65.1 | 64.7 |
-70 | 72.33 | 71.93 | 71.53 | 71.13 | 70.73 | 70.33 | 69.93 | 69.53 | 69.13 | 68.73 |
-60 | 76.33 | 75.93 | 75.53 | 75.13 | 74.73 | 74.33 | 73.93 | 73.53 | 73.13 | 72.73 |
-50 | 80.31 | 79.91 | 79.51 | 79.12 | 78.72 | 78.32 | 77.92 | 77.52 | 77.12 | 76.73 |
°C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
-40 | 84.27 | 83.88 | 83.48 | 83.08 | 82.69 | 82.29 | 81.9 | 81.5 | 81.1 | 80.7 |
-30 | 88.22 | 87.83 | 87.43 | 87.04 | 86.64 | 86.25 | 85.85 | 85.46 | 85.06 | 84.67 |
-20 | 92.16 | 91.77 | 91.37 | 90.98 | 90.59 | 90.19 | 89.8 | 89.4 | 89.01 | 88.62 |
-10 | 96.09 | 95.69 | 95.3 | 94.91 | 94.52 | 94.12 | 93.73 | 93.34 | 92.95 | 92.55 |
0 | 100 | 99.61 | 99.22 | 98.83 | 98.44 | 98.04 | 97.65 | 97.26 | 96.87 | 96.48 |
°C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
0 | 100 | 100.39 | 100.78 | 101.17 | 101.56 | 101.95 | 102.34 | 102.73 | 103.12 | 103.51 |
10 | 103.9 | 104.29 | 104.68 | 105.07 | 105.46 | 105.85 | 106.24 | 106.63 | 107.02 | 107.4 |
20 | 107.79 | 108.18 | 108.57 | 108.96 | 109.34 | 109.73 | 110.12 | 110.51 | 110.9 | 111.28 |
30 | 111.67 | 112.06 | 112.45 | 112.83 | 113.22 | 113.61 | 113.99 | 114.38 | 114.77 | 115.15 |
40 | 115.54 | 115.92 | 116.31 | 116.7 | 117.08 | 117.47 | 117.85 | 118.24 | 118.62 | 119.01 |
°C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
50 | 119.4 | 119.78 | 120.16 | 120.55 | 120.93 | 121.32 | 121.7 | 122.09 | 122.47 | 122.86 |
60 | 123.24 | 123.62 | 124.01 | 124.39 | 124.77 | 125.16 | 125.54 | 125.92 | 126.31 | 126.69 |
70 | 127.07 | 127.45 | 127.84 | 128.22 | 128.6 | 128.98 | 129.36 | 129.75 | 130.13 | 130.51 |
80 | 130.89 | 131.27 | 131.66 | 132.04 | 132.42 | 132.8 | 133.18 | 133.56 | 133.94 | 134.32 |
90 | 134.7 | 135.08 | 135.46 | 135.84 | 136.22 | 136.6 | 136.98 | 137.36 | 137.74 | 138.12 |
°C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
100 | 138.5 | 138.88 | 139.26 | 139.64 | 140.02 | 140.4 | 140.77 | 141.15 | 141.53 | 141.91 |
110 | 142.29 | 142.66 | 143.04 | 143.42 | 143.8 | 144.18 | 144.55 | 144.93 | 145.31 | 145.68 |
120 | 146.06 | 146.44 | 146.82 | 147.19 | 147.57 | 147.94 | 148.32 | 148.7 | 149.07 | 149.44 |
130 | 149.82 | 150.2 | 150.70 | 150.95 | 151.33 | 151.7 | 152.08 | 152.45 | 152.83 | 153.2 |
140 | 153.70 | 153.95 | 154.32 | 154.7 | 155.07 | 155.45 | 155.82 | 156.2 | 156.57 | 156.94 |
°C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
150 | 157.32 | 157.69 | 170.06 | 170.44 | 170.81 | 159.18 | 159.56 | 159.93 | 160.3 | 160.67 |
160 | 161.04 | 161.42 | 161.79 | 162.16 | 162.53 | 162.9 | 163.28 | 163.65 | 164.02 | 164.39 |
170 | 164.76 | 165.13 | 165.5 | 165.88 | 166.24 | 166.62 | 166.99 | 167.32 | 167.73 | 168.1 |
180 | 168.47 | 168.84 | 169.21 | 169.70 | 169.95 | 170.32 | 170.68 | 171.05 | 171.42 | 171.79 |
190 | 172.16 | 172.53 | 172.9 | 173.27 | 173.64 | 174 | 174.37 | 174.74 | 175.11 | 175.48 |
°C | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
200 | 175.84 |
****RTD PT100表顯示了電阻與溫度之間的對(duì)應(yīng)關(guān)系。
圖1. 2線連接時(shí),由于引線電阻與RTD串聯(lián),增大了電阻,會(huì)最終影響測(cè)量精度。
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